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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2019	Nov. 23, 2019
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q3
Entity Registrant Name	Phathom Pharmaceuticals, Inc.
Entity Central Index Key	0001783183
Entity Tax Identification Number	82-4151574
Entity Current Reporting Status	No
Entity Filer Category	Non-accelerated Filer
Entity File Number	001-39094
Entity Shell Company	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Small Business	true
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	2150 E. Lake Cook Road
Entity Address, Address Line Two	Suite 800
Entity Address, City or Town	Buffalo Grove
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60089
City Area Code	(650)
Local Phone Number	325-5156
Entity Common Stock, Shares Outstanding		24,526,537
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	PHAT
Security Exchange Name	NASDAQ

Combined Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 74,484	$ 879
Prepaid expenses and other current assets (including related party amounts of $36 and $19, respectively)	3,169	23
Total current assets	77,653	902
Property, plant and equipment, net	40
Other assets	2,013
Total assets	79,706	902
Current liabilities:
Accounts payable (including related party amounts of $57 and $45, respectively)	439	55
Accrued expenses (including related party amounts of $176 and $2, respectively)	2,120	170
Accrued interest (including related party amounts of $483 and $13, respectively)	2,332	13
Convertible promissory notes payable at fair value (including related party amounts of $21,103 and $1,950, respectively)	95,229	1,950
Warrant liabilities (including related party amounts of ($106,925 and $0, respectively)	107,373
Total current liabilities	207,493	2,188
Long-term debt, net of discount	22,611
Other long-term liabilities	2,063
Total liabilities	232,167	2,188
Commitments and contingencies (Note 3)
Stockholders’ deficit:
Additional paid-in capital	5,952	2
Accumulated deficit	(158,413)	(1,288)
Total stockholders’ deficit	(152,461)	(1,286)
Total liabilities and stockholders’ deficit	$ 79,706	$ 902

Combined Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Prepaid expenses and other current assets, related parties	$ 36	$ 19
Accounts payable, related parties	57	45
Accrued expenses, related parties	176	2
Accrued interest, related parties	483	13
Convertible promissory notes payable at fair value, related parties	21,103	1,950
Warrant liabilities, related parties	$ 106,925	$ 0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, authorized shares	50,000,000
Common stock, issued shares	11,876,518
Common stock, outstanding shares	7,420,989	6,760,334

Combined Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating expenses:
Research and development (includes related party amounts of $207, $0, $207 and $0, respectively)	$ 4,469	$ 6	$ 7,670	$ 6
In-process research and development			78,897
General and administrative (includes related party amounts of $156, $72, $174 and $196, respectively)	1,813	262	3,955	768
Total operating expenses	6,282	268	90,522	774
Loss from operations	(6,282)	(268)	(90,522)	(774)
Other income (expense):
Interest income	429		530
Interest expense (includes related party amounts of $(302), $(4), $(498) and $(8), respectively)	(1,990)	(4)	(3,138)	(8)
Change in fair value of warrant liabilities (includes related party amounts of $(57,754), ($0), ($59,031) and ($0), respectively)	(57,776)		(59,060)
Change in fair value of convertible promissory notes (includes related party amounts of $(732), $(18), $(1,053) and $(22), respectively)	(2,486)	(18)	(4,928)	(22)
Other income (expense)	(7)		(7)
Total other income (expense)	(61,830)	(22)	(66,603)	(30)
Net loss	$ (68,112)	$ (290)	$ (157,125)	$ (804)
Net loss per share, basic and diluted	$ (9.30)	$ (0.04)	$ (22.87)	$ (0.14)
Weighted-average shares of common stock outstanding, basic and diluted	7,326,090	6,760,334	6,871,471	5,812,860

Combined Statements of Operations and Comprehensive Loss (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Research and development expenses, related party	$ 207	$ 0	$ 207	$ 0
General and administrative expenses, related party	156	72	174	196
Interest expense, related party	(302)	(4)	(498)	(8)
Change in fair value of warrant liabilities, related party	(57,754)	0	(59,031)	0
Change in fair value of convertible promissory notes, related party	$ (732)	$ (18)	$ (1,053)	$ (22)

Combined Statement of Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance at Dec. 31, 2017	$ 0	$ 0	$ 0	$ 0
Beginning balance, shares at Dec. 31, 2017		0
Issuance of common stock to founders (unaudited)	2		2
Issuance of common stock to founders (unaudited), shares		2,000
Net loss (unaudited)	(254)			(254)
Ending balance at Mar. 31, 2018	(252)	$ 0	2	(254)
Ending balance, shares at Mar. 31, 2018		2,000
Beginning balance at Dec. 31, 2017	0	$ 0	0	0
Beginning balance, shares at Dec. 31, 2017		0
Net loss (unaudited)	(804)
Ending balance at Sep. 30, 2018	(802)	$ 0	2	(804)
Ending balance, shares at Sep. 30, 2018		2,000
Beginning balance at Dec. 31, 2017	0	$ 0	0	0
Beginning balance, shares at Dec. 31, 2017		0
Issuance of common stock (unaudited), shares		1,000
Ending balance at Dec. 31, 2018	$ (1,286)	$ 0	2	(1,288)
Ending balance, shares at Dec. 31, 2018	6,760,334	0
Beginning balance at Mar. 31, 2018	$ (252)	$ 0	2	(254)
Beginning balance, shares at Mar. 31, 2018		2,000
Net loss (unaudited)	(260)			(260)
Ending balance at Jun. 30, 2018	(512)	$ 0	2	(514)
Ending balance, shares at Jun. 30, 2018		2,000
Net loss (unaudited)	(290)			(290)
Ending balance at Sep. 30, 2018	(802)	$ 0	2	(804)
Ending balance, shares at Sep. 30, 2018		2,000
Beginning balance at Dec. 31, 2018	$ (1,286)	$ 0	2	(1,288)
Beginning balance, shares at Dec. 31, 2018	6,760,334	0
Merger of entities under common control into the Company (unaudited), shares		6,760,334
Vesting restrictions placed on previously issued and outstanding common stock (unaudited), shares		(3,373,408)
Issuance of common stock (unaudited), shares		1,491,072
Vesting of restricted shares (unaudited), shares		1,054,192
Net loss (unaudited)	$ (1,251)			(1,251)
Ending balance at Mar. 31, 2019	(2,537)	$ 0	2	(2,539)
Ending balance, shares at Mar. 31, 2019		5,932,190
Beginning balance at Dec. 31, 2018	$ (1,286)	$ 0	2	(1,288)
Beginning balance, shares at Dec. 31, 2018	6,760,334	0
Net loss (unaudited)	$ (157,125)
Ending balance at Sep. 30, 2019	$ (152,461)	$ 0	5,952	(158,413)
Ending balance, shares at Sep. 30, 2019	7,420,989	7,420,989
Beginning balance at Mar. 31, 2019	$ (2,537)	$ 0	2	(2,539)
Beginning balance, shares at Mar. 31, 2019		5,932,190
Issuance of common stock (unaudited)	5,885		5,885
Issuance of common stock (unaudited), shares		1,084,000
Vesting of restricted shares (unaudited), shares		203,078
Stock-based compensation (unaudited)	29		29
Net loss (unaudited)	(87,762)			(87,762)
Ending balance at Jun. 30, 2019	(84,385)	$ 0	5,916	(90,301)
Ending balance, shares at Jun. 30, 2019		7,219,268
Vesting of restricted shares (unaudited), shares		201,721
Stock-based compensation (unaudited)	36		36
Net loss (unaudited)	(68,112)			(68,112)
Ending balance at Sep. 30, 2019	$ (152,461)	$ 0	$ 5,952	$ (158,413)
Ending balance, shares at Sep. 30, 2019	7,420,989	7,420,989

Combined Statement of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net loss		$ (157,125)	$ (804)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization		2
Stock-based compensation		66
Amortization of debt discount		243
Acquired in-process research and development		78,897
Change in fair value of warrant liabilities (includes related party amounts of $59,031 and $0, respectively)	$ 57,776	59,060
Change in fair value of convertible promissory notes (includes related party amounts of $1,053 and $22, respectively)		4,928	22
Changes in operating assets and liabilities:
Prepaid expenses and other current assets (includes related party amounts of $17, and $8, respectively)		(3,147)	(36)
Accounts payable and accrued expenses (includes related party amounts of $186, and $32, respectively)		1,603	89
Accrued interest (includes related party amounts of $483 and $13, respectively)		2,347	8
Net cash used in operating activities		(13,126)	(721)
Cash flows from investing activities
Cash paid for purchased in-process research and development		(25,118)
Cash paid for property, plant and equipment		(26)
Net cash used in investing activities		(25,144)
Cash flows from financing activities
Proceeds from issuance of common stock			2
Proceeds from issuance of convertible promissory notes		88,324	850
Net proceeds from issuance of long-term debt		24,850
Issuance costs associated with Initial Public Offering (IPO)		(1,299)
Net cash provided by financing activities		111,875	852
Net increase in cash		73,605	131
Cash and cash equivalents – beginning of period		879
Cash and cash equivalents – end of period	$ 74,484	74,484	$ 131
Supplemental disclosure of cash flow information
Interest paid		549
Supplemental disclosure of noncash investing and financing activities
Exchange of accrued interest for convertible promissory notes		27
Issuance of common stock warrants in connection with long-term debt		419
Unpaid initial public offering costs		714
Final interest payment fee		2,063
Takeda License
Supplemental disclosure of noncash investing and financing activities
Issuance of Takeda Warrants in connection with Takeda License		47,894
Issuance of common stock in connection with Takeda License		$ 5,885

Combined Statement of Cash Flows (Unaudited) (Parenthetical) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Statement Of Cash Flows [Abstract]
Change in fair value of warrant liabilities related party	$ 59,031	$ 0
Change in fair value of convertible promissory notes related party	1,053	22
Related parties prepaid expenses and other assets current	17	8
Related parties accounts payable and accrued expenses	186	32
Related parties accrued interest	$ 483	$ 13

Organization, Basis of Presentation and Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization, Basis of Presentation and Summary of Significant Accounting Policies

1. Organization, Basis of Presentation and Summary of Significant Accounting Policies

Organization

Phathom Pharmaceuticals, Inc. (the “Company” or “Phathom”) was incorporated in the state of Delaware in January 2018 under the name North Bridge IV, Inc. On March 13, 2019, the Company changed its name to Phathom Pharmaceuticals, Inc. and merged with YamadaCo IIA, Inc. (“YamadaCo”), a Delaware corporation formed in September 2017, with Phathom being the surviving entity (the “Merger”). All activities of YamadaCo prior to 2018 related to formation and were insignificant. The Company is a late clinical-stage biopharmaceutical company focused on developing and commercializing novel treatments for gastrointestinal diseases.

On October 29, 2019, the Company completed its initial public offering (the “IPO”) and issued 10,997,630 shares of common stock for net proceeds of approximately $191.4 million. Upon the closing of the IPO, the convertible promissory notes payable were converted into 6,107,918 shares of common stock. See Note 7 to these financial statements for additional details.

Stock Split and Conversion

During 2018, without consideration of the forward stock split described immediately below, both the Company and YamadaCo issued 1,000 shares of common stock at a purchase price of $1.00 per share, and had no other capital transactions prior to the Merger. Immediately prior to the Merger, the Company effected a 1,559.1183-for-1 forward stock split for each outstanding share of its common stock and, effective upon the closing of the Merger, each issued and outstanding share of YamadaCo was converted into 1,559.1183 shares of the Company’s common stock. Upon completion of the Merger, the Company had 6,760,334 shares of common stock outstanding, with the prior stockholders of each YamadaCo and Phathom holding an equal number of shares. The accompanying combined financial statements and notes to the combined financial statements give retroactive effect to the forward stock split and conversion for all periods presented.

On October 11, 2019, the Company effected a 2.168-for-1 forward stock split of its common stock (the “Forward Stock Split”). The par value of the common stock was not adjusted as a result of the Forward Stock Split and the authorized shares were increased to 50,000,000 shares of common stock in connection with the Forward Stock Split. The accompanying combined financial statements and notes to the combined financial statements give retroactive effect to the Forward Stock Split for all periods presented, unless otherwise indicated.

Basis of Presentation

The Company’s combined financial statements are prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). The accompanying combined financial statements include the accounts of the Company (the receiving entity) and YamadaCo, prior to the Merger. The Company and YamadaCo were entities under the common control of Frazier Life Sciences IX, L.P. (“Frazier”) as a result of, among others, Frazier’s; (i) ownership of a majority of the outstanding capital stock of both companies, (ii) financing of both companies, (iii) control of board of directors of both companies, and (iv) management of both companies. Both the Company and YamadaCo were formed for the purpose of identifying potential assets around which to form an operating company. As the merged entities were under common control, the combined financial statements report the financial position, results of operations and cash flows of the Company and YamadaCo as though the transfer of net assets and equity interests had occurred at the beginning of 2018. All intercompany accounts and transactions have been eliminated in combination.

Liquidity and Capital Resources

From inception to September 30, 2019, the Company has devoted substantially all of its efforts to organizing and staffing the Company, business planning, raising capital, in-licensing its initial product candidate, vonoprazan, meeting with regulatory authorities, and preparing for the planned Phase 3 clinical trials of vonoprazan. The Company has a limited operating history, has never generated any revenue, and the sales and income potential of its business is unproven. The Company has incurred net losses and negative cash flows from operating activities since its inception and expects to continue to incur net losses into the foreseeable future as it continues the development and commercialization of vonoprazan. From inception to September 30, 2019, the Company has funded its operations through the issuance of convertible promissory notes and commercial bank debt. Additionally, on October 29, 2019, the Company completed its IPO and issued 10,997,630 shares of common stock for net proceeds of approximately $191.4 million.

The accompanying combined financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business, and do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or amounts and classification of liabilities that may result from the outcome of this uncertainty. Management is required to perform a two-step analysis over the Company’s ability to continue as a going concern. Management must first evaluate whether there are conditions and events that raise substantial doubt about the Company’s ability to continue as a going concern (Step 1). If management concludes that substantial doubt is raised, management is also required to consider whether its plans alleviate that doubt (Step 2).

Upon the initial public filing that took place on October 29, 2019, management believes that it has sufficient working capital on hand to fund operations through at least the next twelve months from the date these combined financial statements were available to be issued. There can be no assurance that the Company will be successful in acquiring additional funding, that the Company’s projections of its future working capital needs will prove accurate, or that any additional funding would be sufficient to continue operations in future years.

Use of Estimates

The preparation of the Company’s combined financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the Company’s combined financial statements and accompanying notes. The most significant estimates in the Company’s combined financial statements relate to accruals for research and development expenses, and the valuation of convertible promissory notes, warrant liabilities and various other equity instruments. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results could differ materially from those estimates and assumptions.

Unaudited Interim Financial Information

The accompanying interim balance sheet as of September 30, 2019, the combined statements of operations and cash flows for the three and nine months ended September 30, 2019 and 2018 and the combined statement of stockholders’ deficit for the three and nine months ended September 30, 2019 and 2018 and the related footnote disclosures are unaudited. In management’s opinion, the unaudited interim financial statements have been prepared on the same basis as the audited combined financial statements and include all adjustments, which include only normal recurring adjustments, necessary for the fair presentation of the Company’s financial position as of September 30, 2019 and its results of operations and cash flows for the three and nine months ended September 30, 2019 and 2018 in accordance with GAAP. The results for the nine months ended September 30, 2019 are not necessarily indicative of the results expected for the full fiscal year or any other interim period.

Fair Value Option

As permitted under Accounting Standards Codification (“ASC”) 825, Financial Instruments, (“ASC 825”), the Company has elected the fair value option to account for its convertible promissory notes issued since inception. In accordance with ASC 825, the Company records these convertible promissory notes at fair value with changes in fair value recorded in the combined statements of operations. As a result of applying the fair value option, direct costs and fees related to the convertible promissory notes were recognized in earnings as incurred and not deferred.

Fair Value Measurements

The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or non-recurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

Level 1: Observable inputs such as quoted prices in active markets.

Level 2: Inputs, other than the quoted prices in active markets that are observable either directly or indirectly.

Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

The carrying amounts of the Company’s financial instruments, including cash and cash equivalents classified within the Level 1 designation discussed above, prepaid and other current assets, accounts payable, and accrued liabilities, approximate fair value due to their short maturities. Warrant liabilities and convertible promissory notes are recorded at fair value on a recurring basis.

The Company has no financial assets measured at fair value on a recurring basis. None of the Company’s non-financial assets or liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented.

Liabilities measured at fair value on a recurring basis are as follows (in thousands):

			Fair Value Measurements at Reporting Date Using:
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2018:
Convertible promissory notes	$	1,950	$	—	$	—	$	1,950

As of September 30, 2019:
Warrant liabilities	$	107,373	$	—	$	—	$	107,373
Convertible promissory notes		95,229		—		—		95,229
Total	$	202,602	$	—	$	—	$	202,602

The warrant liabilities consist of an issued and outstanding common stock warrant (the “Takeda Warrant”) and a right to receive an additional common stock warrant (the “Takeda Warrant Right”, and together with the Takeda Warrant, the “Takeda Warrants”) issued to Takeda Pharmaceutical Company Limited (“Takeda”) in connection with a May 2019 license agreement (see Note 3) and warrants (the “Lender Warrants”) issued in connection with a loan and security agreement for commercial bank debt (see Note 5). The Takeda Warrants are accounted for as liabilities as they do not meet all the conditions for equity classification due to (i) insufficient authorized shares for the Takeda Warrant and (ii) the Takeda Warrant Right is not indexed to the Company’s own stock. The Lender Warrants are accounted for as liabilities as they contain a holder put right under which the lenders could require the Company to pay cash in exchange for the warrants. The fair value of the Takeda Warrants is derived from the model used to estimate the fair value the Company’s common stock (see Note 6). The fair value of the Lender Warrants is estimated using a probability-weighted model considering IPO and non-IPO scenarios. The IPO scenarios utilize a binomial lattice model to estimate a distribution of total equity values as of a projected IPO date. The non-IPO scenario utilizes the repurchase price associated with the warrant put right discounted to present value based on venture capital rates of return and the term associated with the put right. As of September 30, 2019, the fair value of the Takeda Warrants was $107.0 million and the fair value of the Lender Warrants was $0.4 million.

As further described in Note 4, the Company issued convertible promissory notes to Frazier (the “Frazier Notes”) from January 2018 to April 2019 and issued convertible promissory notes in May 2019 (the “May 2019 Notes”) to investors including Frazier. The Company has elected the fair value option for each of its convertible promissory note issuances. The fair value of the Frazier Notes was estimated using a scenario-based analysis that estimated the fair value of the convertible promissory notes based on the probability-weighted present value of expected future investment returns, considering possible outcomes available to the noteholders, including conversions in subsequent equity financings, change of control transactions, settlement and dissolution. The fair value of the May 2019 Notes is estimated using a scenario-based analysis that estimates the fair value of the convertible promissory notes based on the probability-weighted present value of expected future investment returns, considering each of the possible outcomes available to the noteholders, including various IPO, settlement, equity financing, corporate transaction and dissolution scenarios. As of December 31, 2018, the fair value of the Frazier Notes was $2.0 million and the Frazier Notes were exchanged for May 2019 Notes in May 2019. As of September 30, 2019, the fair value of the May 2019 Notes was $95.2 million.

The Company adjusts the carrying value of its warrant liabilities and convertible promissory notes to their estimated fair value at each reporting date, with any related increases or decreases in the fair value recorded as change in fair value of warrant liabilities and change in fair value of convertible promissory notes, respectively, in the combined statements of operations.

Liability

At initial

valuation

date

Fair value

as of

September 30,

Fair value method

at initial

valuation date

(and relative weighting)

Fair value

method at as of

September 30, 2019 (and

relative weighting)

KEY unobservable inputs

Range

Takeda Warrants

47,894

107,373

Financing transactions (40%)

Income approach (60%)

Financing transactions (70%)

Income approach (30%)

Transaction prices per share

Estimated time to liquidity

Discount rate

$9.33 - $18.56

0.09 - 1.77 years

7.5%

May 2019 Notes

90,250

95,229

Financing transactions (40%)

Income approach (60%)

Financing transactions (70%)

Income approach (30%)

Estimated time to liquidity

Volatility

Discount rate

0.09 - 1.77 years

65%

22.6% - 25%

The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs (in thousands):

	Warrant Liabilities		Convertible Promissory Notes
Balance at January 1, 2018	$	—	$	—
Issuance of convertible promissory notes		—		1,900
Change in fair value		—		50
Balance at December 31, 2018		—		1,950
Issuance of convertible promissory notes		—		90,750
Exchange of convertible promissory notes (Note 4)		—		(2,399	)
Issuance of warrants		48,313		—
Change in fair value		59,060		4,928
Balance at September 30, 2019	$	107,373	$	95,229

Cash and Cash Equivalents

The Company considers all highly liquid investments with original maturities of three months or less when purchased to be cash equivalents. Cash and cash equivalents include cash in readily available checking accounts and money market funds.

Concentrations of Credit Risk

Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash and cash equivalents. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held.

Deferred Offering Costs

The Company has deferred offering costs consisting of legal, accounting and other fees and costs directly attributable to its planned IPO. The deferred offering costs will be offset against the proceeds received upon the completion of the planned IPO. In the event the planned IPO is terminated, all of the deferred offering costs will be expensed within the Company’s statements of operations. As of September 30, 2019, $2.0 million of deferred offering costs were recorded within other long-term assets on the balance sheet. No such costs were included on the combined balance sheet as of December 31, 2018.

Research and Development Expenses and Accruals

All research and development costs are expensed in the period incurred and consist primarily of salaries, payroll taxes, employee benefits, stock-based compensation charges for those individuals involved in research and development efforts, external research and development costs incurred under agreements with contract research organizations and consultants to conduct and support the Company’s planned clinical trials of vonoprazan, and costs related to manufacturing vonoprazan for clinical trials.

The Company has entered into various research and development contracts with clinical research organizations, clinical manufacturing organizations and other companies. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred, and payments made in advance of performance are reflected in the accompanying balance sheets as prepaid expenses or accrued liabilities. The Company records accruals for estimated costs incurred for ongoing research and development activities. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the services, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the prepaid or accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates.

In-Process Research and Development

The Company evaluates whether acquired intangible assets are a business under applicable accounting standards. Additionally, the Company evaluates whether the acquired assets have a future alternative use. Intangible assets that do not have future alternative use are considered acquired in-process research and development. When the acquired in-process research and development assets are not part of a business combination, the value of the consideration paid is expensed on the acquisition date. Future costs to develop these assets are recorded to research and development expense as they are incurred.

Stock-Based Compensation

Stock-based compensation expense represents the cost of the grant date fair value of equity awards recognized over the requisite service period of the awards (generally the vesting period) on a straight-line basis. The Company recognizes forfeitures as they occur.

Comprehensive Loss

Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. The Company’s comprehensive loss was the same as its reported net loss for all periods presented.

Segment Reporting

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions on how to allocate resources and assess performance. The Company views its operations and manages its business as one operating segment.

Net Loss Per Share

For the three and nine months ended September 30, 2018 and 2019, the net loss per share was recast to include in the numerator the net losses of both the Company and YamadaCo and include in the denominator the combined weighted-average outstanding shares of both the Company and YamadaCo. Basic net loss per share is computed by dividing the combined net loss by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. The Company has excluded weighted-average unvested shares of 4,550,428 and 3,342,544 shares from the weighted-average number of common shares outstanding for the three and nine months ended September 30, 2019. No shares of common stock were unvested during the year ended September 30, 2018. Diluted net loss per share is computed by dividing the combined net loss by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Dilutive common stock equivalents are comprised of unvested common stock, options, warrants and convertible promissory notes. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding as inclusion of the potentially dilutive securities would be antidilutive.

The following potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented because their inclusion would have been antidilutive:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Warrants		7,588,000		—		7,588,000		—
Stock options		1,400,528		—		1,400,528		—
Shares subject to repurchase		4,550,428		—		3,342,544		—

Recently Adopted Accounting Pronouncements

In June 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting. This guidance expands the scope of Topic 718, Compensation—Stock Compensation, which currently only includes share-based payments to employees, to include share-based payments issued to nonemployees for goods or services. Consequently, the accounting for share-based payments to nonemployees and employees will be substantially aligned. This ASU supersedes Subtopic 505-50, Equity—Equity-Based Payments to Non-Employees and is effective for public companies for annual periods beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted as long as ASU No. 2014-09 has been adopted by the Company. The Company adopted this guidance effective January 1, 2018, and the adoption did not have a material impact on the Company's financial statements.

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), which requires a lessee to recognize a lease liability and a right-of-use asset for all leases with lease terms of more than 12 months. Additionally, certain qualitative and quantitative disclosures will be required in the financial statements. This guidance is effective for annual reporting periods beginning after December 15, 2018, including interim periods within those fiscal years, and early adoption is permitted. Companies may adopt this guidance using a modified retrospective approach for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements. The Company adopted this guidance effective January 1, 2018, and the adoption did not have any impact on the Company’s financial statements as the Company did not have any leases at the time of adoption. As the Company enters into future, material lease agreements, the adoption of this guidance is expected to result in a significant increase in the total assets and liabilities reported on the balance sheets.

Recently Issued Accounting Pronouncements

In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which eliminates, modifies and adds disclosure requirements on fair value measurements. The standard is effective for annual periods beginning after December 15, 2019, including interim periods within those fiscal years, and early adoption is permitted. The Company is currently evaluating the impact the adoption of ASU No. 2018-13 will have on the Company’s financial statements.

Related Party Transactions

9 Months Ended

Sep. 30, 2019

Related Party Transactions

2. Related Party Transactions

Frazier is a principal stockholder of the Company and is represented on the Company’s board of directors. For the year ended December 31, 2018 and the nine months ended September 30, 2019, the Company conducted its operations within office space controlled by Frazier and Frazier allocated a portion of the costs associated with this office to the Company. In addition, Frazier paid for various goods and services, such as employee wages, insurance and expense reimbursements and various administrative services associated with the operations of the Company and charged the Company for those expenses. As of September 30, 2019, and December 31, 2018, the Company had outstanding accounts payable balances due to Frazier of $71,000 and $45,000, respectively, related to these shared operating expenses. For the three months ended September 30, 2019 and 2018, the Company incurred $0.2 million and $66,000, respectively, of shared operating expenses. For the nine months ended September 30, 2019 and 2018, the Company incurred $0.3 million and $0.2 million, respectively, of shared operating expenses. In addition to the shared operating expenses, the Company issued convertible promissory notes to Frazier during 2018 and 2019 (see Note 4).

Frazier is a principal stockholder in PCI Pharma Services (“PCI”). In the third quarter of 2019, the Company engaged PCI for clinical manufacturing services. As of September 30, 2019, the Company had $0.1 million in prepaid services and $0.2 million outstanding accounts payable and accrued expenses related to these manufacturing services. For the three and nine months ended September 30, 2019, the Company incurred $0.2 million of expenses related to services performed by PCI.

Mountain Field LLC (“Mountain Field”) is an entity owned by the chairman of the Company’s board of directors. During the year ended December 31, 2018 and the nine months ended September 30, 2019, the Company charged Mountain Field for certain rent and payroll related expenses. These shared expenses were allocated based on usage of the related facilities and time incurred by personnel. As of September 30, 2019, and December 31, 2018, the Company had an outstanding accounts receivable balance from Mountain Field of $0 and $19,000, respectively, related to shared operating expenses. For the three months ended September 30, 2019 and 2018, the Company incurred $0 and $5,000, respectively, for shared expenses. For the nine months ended September 30, 2019 and 2018, the Company charged Mountain Field $0.1 million and $2,000, respectively, for shared expenses.

Takeda became a common stockholder of the Company as of May 7, 2019 in connection with the May 2019 license agreement (see Note 3).

Commitments and Contingencies

9 Months Ended

Sep. 30, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

3. Commitments and Contingencies

License Agreement

On May 7, 2019, the Company entered into a license agreement with Takeda pursuant to which it was granted an exclusive license to commercialize vonoprazan fumarate in the United States, Canada and Europe (the “Takeda License”). The Company also has the right to sublicense its rights under the agreement, subject to certain conditions. The agreement will remain in effect, on a country-by-country and product-by-product basis, until the later of (i) the expiration of the last to expire valid patent claim covering vonoprazan fumarate alone or in combination with at least one other therapeutically active ingredient, (ii) the expiration of the applicable regulatory exclusivity and (iii) 15 years from the date of first commercial sale, unless earlier terminated. The Company may terminate the Takeda License upon six months’ written notice. The Company and Takeda may terminate the Takeda License in the case of the other party’s insolvency or material uncured breach. Takeda may terminate the Takeda License if the Company challenges, or assists in challenging, licensed patents.

In consideration of the Takeda License, the Company (i) paid Takeda $25.0 million in cash, (ii) issued Takeda 1,084,000 shares of its common stock at a fair value of $5.9 million, (iii) issued the Takeda Warrant to purchase 7,588,000 shares of its common stock at an exercise price of $0.00004613 per share at an initial fair value of $47.9 million, and (iv) issued the Takeda Warrant Right to receive an additional common stock warrant should Takeda’s fully-diluted ownership of the Company represent less than a certain specified percentage of the fully-diluted capitalization, including shares issuable upon conversion of outstanding convertible promissory notes, calculated immediately before the closing of the Company’s IPO, with a nominal initial fair value due to the low probability of issuance. The Takeda Warrant Right expired upon completion of our IPO, and no additional warrant was issued. In addition, the Company is obligated to pay Takeda up to an aggregate of $250.0 million in sales milestones upon the achievement of specified levels of product sales, and a low double-digit royalty rate on aggregate net sales of licensed products, subject to certain adjustments. The Company incurred $0.1 million of transaction costs in connection with the Takeda License. The Takeda Warrant has an exercise price of $0.00004613 per share, expires on May 7, 2029 and becomes exercisable upon (i) certain change of control transactions of the Company or (ii) the consummation of an IPO by the Company.

The transaction has been accounted for as an asset acquisition as substantially all of the fair value is concentrated in a group of similar assets. The $78.9 million fair value of the consideration paid for these research and development assets, which have no alternative future use, was recorded as in-process research and development in the Company’s combined statement of operations for the nine months ended September 30, 2019.

Contingencies

In the event the Company becomes subject to claims or suits arising in the ordinary course of business, the Company would accrue a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated.

Convertible Promissory Notes

9 Months Ended

Sep. 30, 2019

Debt Disclosure [Abstract]

Convertible Promissory Notes

4. Convertible Promissory Notes

Frazier Convertible Note Financing

From January 2018 to April 2019, the Company issued the Frazier Notes for an aggregate of $2.4 million and bearing interest at per annum rates ranging from 1.68% to 2.55%. Of the Frazier Notes, $1.9 million were issued in 2018 and $0.5 million were issued in April 2019. Due to certain embedded features within the Frazier Notes, the Company elected to account for these notes and all their embedded features under the fair value option. The Company recorded changes in the fair value of the Frazier Notes in the combined statements of operations until May 2019, when the Frazier Notes and related accrued interest were exchanged, at their then fair value of $2.4 million, for the May 2019 Notes. For the three and nine months ended September 30, 2018, and the nine months ended September 30, 2019, the Company recognized $18,000 of expense, $22,000 of expense, and $50,000 of income, respectively, in change in fair value of convertible promissory notes in the combined statements of operations related to changes in the fair value of the Frazier Notes. For the three and nine months ended September 30, 2018 and the nine months ended September 30, 2019, the Company recognized $4,000, $8,000 and $15,000, respectively, of interest expense in connection with the Frazier Notes. No interest expense or changes in fair value related to the Frazier Notes were recorded in the three months ended September 30, 2019, as the Frazier Notes were exchanged in May 2019.

May 2019 Convertible Note Financing

In May 7, 2019, the Company entered into a note purchase agreement under which it issued the unsecured May 2019 Notes for an aggregate of $90.3 million, resulting in gross proceeds to the Company of $87.8 million in cash and $2.4 million related to the exchange of the Frazier Notes and related accrued interest for the May 2019 Notes. Including the conversion of the Frazier Notes, Frazier purchased $20.0 million of the May 2019 Notes. The May 2019 Notes bear interest at a rate of 6% per annum and are subordinated to borrowings under the Company’s loan and security agreement (see Note 5). The May 2019 Notes become payable upon demand of the holders of at least 60% of the outstanding principal amount of the May 2019 Notes, including Frazier, on May 7, 2020 (the “Maturity Date”), and become due and payable on May 7, 2022, subject to earlier conversion or repayment in the event the Company completes certain equity financings or a change of control. The May 2019 Notes can be converted/redeemed as follows (i) automatically converted upon a qualified equity financing, with a conversion price of the lesser of 80% of the price paid per share in such financing or the conversion cap price per share, (ii) optionally converted upon a non-qualified equity financing with a conversion price of 80% of the price paid per share in such financing, (iii) optionally converted any time after the Maturity Date, with a conversion price per share of the conversion cap price per share, (iv) automatically upon an IPO with a conversion price per share of the lesser of 80% of the IPO price per share, or the conversion cap price per share, and (v) upon certain corporate transactions, receive cash equal to the greater of (A) two times the then outstanding principal and accrued interest and (B) an amount equal to the amount that would be received as if the May 2019 Notes were converted with a conversion price of the conversion cap price per share. The conversion cap price per share is defined as $500.0 million less the outstanding principal and accrued interest divided by the total of (1) the total number of common shares outstanding immediately prior to conversion, (2) the number of common shares issuable upon exercise or conversion of exercisable or convertible securities, and (3) the number of shares of capital stock reserved for issuance under the Company’s equity incentive plan.

The note purchase agreement includes, among others, covenants related to delivery of certain financial reports, certain registration rights, voting provisions regarding the composition of the Company’s board of directors, and limitations on the Company’s ability to pay dividends, incur additional indebtedness or consummate certain changes of control. The note purchase agreement also contains customary events of default, including bankruptcy, the failure to make payments when due, and certain material adverse changes. Upon the occurrence of an event of default, subject to any specified cure periods, all amounts owed by the Company may be declared immediately due and payable. As of September 30, 2019, the Company was in compliance with all applicable covenants under the note purchase agreement.

Due to certain embedded features within the May 2019 Notes, the Company elected to account for these notes and all their embedded features under the fair value option. For the three and nine months ended September 30, 2019, the Company recognized $2.5 million and $4.9 million respectively, of other expense in the combined statements of operations related to increases in the fair value of the May 2019 Notes. For the three and nine months ended September 30, 2019, the Company recognized $1.4 million and $2.2 million, respectively, of interest expense in connection with the May 2019 Notes. As of September 30, 2019, the outstanding principal and accrued interest on the May 2019 Notes was $90.3 million and $2.2 million, respectively. The principal and accrued interest of the May 2019 Notes automatically converted upon the IPO on October 29, 2019, converting into 6,107,918 shares of common stock; refer to Note 7 for further information.

Long-Term Debt

9 Months Ended

Sep. 30, 2019

Debt Disclosure [Abstract]

Long-Term Debt

5. Long-Term Debt

Long-term debt consists of the following (in thousands):

	September 30, 2019
Long-term debt	$	25,000
Unamortized debt discount		(2,389	)
Long-term debt, net of debt discount	$	22,611

On May 14, 2019, the Company entered into a loan and security agreement (the “Loan Agreement”, and all amounts borrowed thereunder the “Term Loans”) with Silicon Valley Bank (“SVB”), as administrative and collateral agent, and lenders including SVB and WestRiver Innovation Lending Fund VIII, L.P. (“WestRiver”). The Company borrowed $25.0 million (“Term Loan A”) at the inception of the Loan Agreement and has the right to borrow an additional $25.0 million (“Term Loan B”). Term Loan B is available through March 31, 2020, provided that (i) the Company has received at least $150.0 million of net cash proceeds in connection with the issuance and sale, subsequent to April 1 2019, of its equity securities and subordinated debt, (ii) the Company has initiated Phase 3 clinical trials for vonoprazan, and (iii) no event of default has occurred.

The Term Loans bear interest at a floating rate of the higher of the Wall Street Journal Prime rate plus 1.75% (7.25% at September 30, 2019) or 7.25%. The monthly payments consist of interest-only through June 1, 2021 or, in the event of positive data with respect to the Company’s Phase 3 clinical trial in both indications for vonoprazan sufficient to file an NDA with the FDA, through June 1, 2022. Subsequent to the interest-only period, the Term Loans will be payable in equal monthly installments of principal, plus accrued and unpaid interest through the maturity date of May 1, 2024. In addition, the Company is obligated to pay a final payment fee of 8.25% of the original principal amount of the Term Loans. As of September 30, 2019, the final payment fee of $2.1 million has been recorded as an other long-term liability.

The Company may elect to prepay all or a portion of the Term Loans prior to maturity, subject to a prepayment fee of up to 2.0% of the then outstanding principal balance and payment of a pro rata portion of the final payment fee. After repayment, no Term Loan amounts may be borrowed again.

The borrowings under the Loan Agreement are collateralized by substantially all of the Company’s assets, excluding intellectual property and certain other assets. The Loan Agreement includes affirmative and negative covenants. The affirmative covenants include, among others, covenants requiring the Company to maintain its legal existence and governmental approvals, deliver certain financial reports, maintain insurance coverage and satisfy certain requirements regarding its operating accounts. The negative covenants include, among others, limitations on the Company’s ability to incur additional indebtedness and liens, merge with other companies or consummate certain changes of control, acquire other companies, engage in new lines of business, make certain investments, pay dividends, transfer or dispose of assets, amend certain material agreements or enter into various specified transactions. The Loan Agreement also contains customary events of default, including bankruptcy, the failure to make payments when due, and a material adverse change. Upon the occurrence of an event of default, subject to any specified cure periods, all amounts owed by the Company would begin to bear interest at a rate that is 4.00% above the rate effective immediately before the event of default and may be declared immediately due and payable by SVB, as collateral agent. As of September 30, 2019, the Company was in compliance with all applicable covenants under the Loan Agreement.

In connection with the Loan Agreement, the Company issued the Lender Warrants to purchase stock of the Company. The Lender Warrants become exercisable only if the Company borrows Term Loan B, and the number, class and per share price of the shares subject to the warrants is dependent on the terms of certain future equity financing transactions of the Company, including an IPO. The Lender Warrants expire ten years from the date of issuance, subject to earlier termination on September 30, 2020 if the Company does not draw down Term Loan B on or before March 31, 2020. The Lender Warrants include a put option pursuant to which, in the event that the Company does not draw down Term Loan B on or before March 31, 2020, the warrant holders may require that the Company repurchase the warrants for a total aggregate repurchase price of $0.5 million. The put right is exercisable through September 30, 2020.

The initial $0.4 million fair value of the Lender Warrants, the $2.1 million final payment fee and $0.2 million of debt issuance costs have been recorded as debt discount and are being amortized to interest expense using the effective interest method over the term of the Term Loans. For the three and nine months ended September 30, 2019, the Company recognized $0.6 million and $0.9 million of interest expense, including amortization of the debt discount, in connection with the Loan Agreement. As of September 30, 2019, the Company had outstanding Term Loans of $25.0 million and accrued interest of $0.2 million.

Future minimum principal and interest payments under the Term Loans, including the final payment fee, as of September 30, 2019 are as follows (in thousands):

Year ending December 31:
2019	$	458
2020		1,843
2021		6,609
2022		9,533
2023		8,920
2024		5,599
Total principal and interest payments		32,962
Less interest and final payment fee		(7,962	)
Long-term debt	$	25,000

Stockholders' Deficit

9 Months Ended

Sep. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stockholders’ Deficit

6. Stockholders’ Deficit

Common Stock

In March 2019, subsequent to the Merger, the Company sold 1,491,072 shares of the Company’s common stock to Frazier.

In March 2019, the founders granted the Company a repurchase right for the 3,373,408 shares of common stock originally purchased in 2018. The Company has the right, but not the obligation, to repurchase unvested shares in the event the founder’s relationship with the Company is terminated, subject to certain limitations, at the original purchase price of the stock. The repurchase right lapsed for 843,352 shares in March 2019 and the repurchase right for the remaining 2,530,056 shares lapses in equal monthly amounts over the following 48-month period ending in March 2023. The fair value of the founder shares at the date the repurchase right was granted is being recognized as stock-based compensation expense on a straight-line basis over the vesting period. As of September 30, 2019, 2,213,808 shares of common stock were subject to repurchase by the Company and the associated repurchase liability was not significant. The amount of recognized and unrecognized stock-based compensation related to the founder stock was immaterial for all periods presented.

In May 2019, the Company issued Takeda 1,084,000 shares of common stock in connection with the Takeda License.

For the period from January 1, 2019 to May 6, 2019, the Company issued 2,524,852 shares of common stock to various employees and consultants of the Company for aggregate proceeds of approximately $1,000. Upon issuance, these shares were subject to a repurchase option by the Company at the original purchase price of the shares. The repurchase rights generally lapse as to 25% of the shares on the first anniversary of the vesting commencement date, and the repurchase right lapses as to 1/48th of the shares each one-month period thereafter, subject to the purchaser remaining continuously an employee, consultant or director of the Company.

On October 29, 2019, the Company completed its IPO and issued 10,997,630 shares of common stock for net proceeds of approximately $191.4 million.

Equity Incentive Plan

The Company’s 2019 Equity Incentive Plan (the “Existing Incentive Plan”) provides for the grant of incentive stock options, non-statutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, and other stock awards to eligible recipients, including employees, directors or consultants of the Company. As of September 30, 2019, the Company had 2,231,739 shares of common stock authorized for issuance under the Existing Incentive Plan, of which 814,951 shares remained available for grant. In May 2019, the Company issued 16,260 shares of common stock under a restricted stock award, of which 6,775 were unvested as of September 30, 2019. For the nine months ended September 30, 2019, 1,400,258 stock options and 16,260 restricted stock awards were granted under the Existing Incentive Plan.

A summary of the Company’s unvested shares is as follows:

Balance at January 1, 2019	—
Vesting restrictions placed on previously issued shares	3,373,408
Sale of unvested common stock	2,524,852
Issuance of unvested restricted stock awards	16,260
Share vesting	(1,458,985	)
Balance at September 30, 2019	4,455,535

For accounting purposes, unvested shares of common stock are considered issued, but not outstanding until they vest.

Stock Options

The fair value of each employee and non-employee stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company, prior to the IPO on October 29, 2019, is a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected volatility based on the historical volatility of a publicly traded set of peer companies. Due to the lack of historical exercise history, the expected term of the Company’s stock options for employees has been determined utilizing the “simplified” method for awards. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

A summary of the Company’s stock option activity and related information is as follows:

	Options Outstanding		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term		Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2018		—
Options granted		1,400,528	$	9.10		—		—
Options exercised and shares vested		—		—		—		—
Options cancelled		—		—		—		—
Balance at September 30, 2019		1,400,528	$	9.10		9.94	$	5,575
Options exercisable as of September 30, 2019		—		—		—		—

The estimated weighted-average fair value of employee and nonemployee director stock options granted during 2019 was $5.12. As of September 30, 2019, the Company had $3.8M of unrecognized stock-based compensation expense, which is expected to be recognized over a weighted-average period of 3.72 years.

Valuation Assumptions

The weighted-average assumptions used to estimate the fair value of stock options using the Black-Scholes option valuation model and the resulting weighted average fair value of stock options granted were as follows:

	Nine Months Ended September 30,
	2019			2018
Assumptions:
Expected term (in years)		6.07			—
Expected volatility		60.17	%		—
Risk free interest rate		1.58	%		—
Dividend yield		—			—

Stock-Based Compensation Expense

Stock-based compensation expense recognized for all equity awards, including founder stock, has been reported in the combined statements of operations as follows (in thousands):

	Three Months Ended September 30, 2019		Nine Months Ended September 30, 2019
Research and development expense	$	8	$	8
General and administrative expense		29		58
Total	$	37	$	66

For the three and nine months ended September 30, 2019, the vested fair value of the restricted stock awards was $37,000 and $66,000, respectively. There was no stock-based compensation expense for the nine months ended September 30, 2018.

Subsequent Events

9 Months Ended

Sep. 30, 2019

Subsequent Events [Abstract]

Subsequent Events

7. Subsequent Events

Reclassification of Takeda Warrant

On October 11, 2019, the Company increased its authorized shares to 50,000,000. As a result, there were sufficient authorized shares for the Takeda Warrant. The Company will record an adjustment to the fair value of the Takeda Warrant as of October 11, 2019 and reclassify the balance from warrant liabilities to additional paid-in capital.

Initial Public Offering

On October 29, 2019, the Company completed its IPO whereby it sold 10,997,630 shares of common stock at a public offering price of $19.00 per share. In aggregate, the Company received net proceeds of approximately $191.4 million, after deducting underwriting discounts, commissions and offering costs of $17.6 million.

In addition, each of the following occurred in connection with the completion of our IPO on October 29, 2019:

•

the issuance of 6,107,918 shares of common stock upon the automatic conversion of the May 2019 Notes;

•

the expiration of the right granted to Takeda to receive an additional common stock warrant, or the Takeda Warrant Right.

The following table summarizes certain actual balance sheet data and pro forma balance sheet data to reflect the activities related to the Company’s IPO noted above, as of September 30, 2019 (in thousands):

	September 30, 2019			Pro forma September 30, 2019
Cash and cash equivalents	$	74,484		$	267,164
Prepaid expenses and other current assets		3,169			3,169
Property, plant and equipment, net		40			40
Other assets		2,013			—
Accounts payable and accrued expenses		4,891			1,996
Convertible promissory notes payable		95,229			—
Warrant liabilities		107,373			448
Long-term liabilities		24,674			24,674
Common stock		—			2
Additional paid in capital		5,952			401,665
Accumulated deficit		(158,413	)		(158,413	)
Total stockholder’s (deficit) equity		(152,461	)		243,254

In connection with the closing of its IPO on October 29, 2019, the Company will record an additional non-cash charge related to the final fair value adjustment of the convertible promissory notes payable. This final fair value adjustment is excluded from the table above.

2019 Incentive Award Plan

In October 2019, the board of directors adopted, and the Company’s stockholders approved the 2019 Equity Incentive Plan (the “2019 Plan”), which will become effective in connection with the IPO. Under the 2019 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units and other awards to individuals who are then employees, officers, non-employee directors or consultants of the Company or its subsidiaries. An aggregate of 2,700,000 shares of the Company’s common stock will initially be available for issuance under awards granted pursuant to the 2019 Plan. The number of shares initially available for issuance will be increased by (i) the number of shares subject to stock options or similar awards granted under the Existing Incentive Plan that expire or otherwise terminate without having been exercised in full after the effective date of the 2019 Plan and unvested shares issued pursuant to awards granted under the Existing Incentive Plan that are forfeited to or repurchased by the Company after the effective date of the 2019 Plan, with the maximum number of shares to be added to the 2019 Plan pursuant to clause (i) above equal to 1,416,788 shares, and (ii) an annual increase on January 1 of each calendar year beginning in 2020 and ending in 2029, equal to the lesser of (a) 5% of the shares of common stock outstanding on the final day of the immediately preceding calendar year and (b) such smaller number of shares as determined by the board of directors.

Approval of the Employee Stock Purchase Plan

In October 2019, the board of directors adopted, and the Company’s stockholders approved, the Employee Stock Purchase Plan (the “ESPP”), which will become effective in connection with the IPO. The ESPP permits participants to purchase common stock through payroll deductions of up to 20% of their eligible compensation, which includes a participant’s gross base compensation for services to the Company, including overtime payments and excluding sales commissions, incentive compensation, bonuses, expense reimbursements, fringe benefits and other special payments. A total of 270,000 shares of common stock is initially reserved for issuance under the ESPP. In addition, the number of shares available for issuance under the ESPP will be annually increased on January 1 of each calendar year beginning in 2020 and ending in 2029, by an amount equal to the lesser of: (i) 1% of the shares outstanding on the final day of the immediately preceding calendar year and (ii) such smaller number of shares as is determined by the board of directors.

Organization, Basis of Presentation and Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Stock Split and Conversion

Basis of Presentation

Liquidity and Capital Resources

Use of Estimates

Unaudited Interim Financial Information

Fair Value Option

Fair Value Measurements

Level 1: Observable inputs such as quoted prices in active markets.

Level 2: Inputs, other than the quoted prices in active markets that are observable either directly or indirectly.

Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.

Liabilities measured at fair value on a recurring basis are as follows (in thousands):

			Fair Value Measurements at Reporting Date Using:
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2018:
Convertible promissory notes	$	1,950	$	—	$	—	$	1,950

As of September 30, 2019:
Warrant liabilities	$	107,373	$	—	$	—	$	107,373
Convertible promissory notes		95,229		—		—		95,229
Total	$	202,602	$	—	$	—	$	202,602

Liability

At initial

valuation

date

Fair value

as of

September 30,

Fair value method

at initial

valuation date

(and relative weighting)

Fair value

method at as of

September 30, 2019 (and

relative weighting)

KEY unobservable inputs

Range

Takeda Warrants

47,894

107,373

Financing transactions (40%)

Income approach (60%)

Financing transactions (70%)

Income approach (30%)

Transaction prices per share

Estimated time to liquidity

Discount rate

$9.33 - $18.56

0.09 - 1.77 years

7.5%

May 2019 Notes

90,250

95,229

Financing transactions (40%)

Income approach (60%)

Financing transactions (70%)

Income approach (30%)

Estimated time to liquidity

Volatility

Discount rate

0.09 - 1.77 years

65%

22.6% - 25%

The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs (in thousands):

	Warrant Liabilities		Convertible Promissory Notes
Balance at January 1, 2018	$	—	$	—
Issuance of convertible promissory notes		—		1,900
Change in fair value		—		50
Balance at December 31, 2018		—		1,950
Issuance of convertible promissory notes		—		90,750
Exchange of convertible promissory notes (Note 4)		—		(2,399	)
Issuance of warrants		48,313		—
Change in fair value		59,060		4,928
Balance at September 30, 2019	$	107,373	$	95,229

Cash and Cash Equivalents

Concentrations of Credit Risk

Deferred Offering Costs

Research and Development Expenses and Accruals

In-Process Research and Development

Stock-Based Compensation

Comprehensive Loss

Segment Reporting

Net Loss Per Share

The following potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented because their inclusion would have been antidilutive:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Warrants		7,588,000		—		7,588,000		—
Stock options		1,400,528		—		1,400,528		—
Shares subject to repurchase		4,550,428		—		3,342,544		—

Recently Adopted and Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements

Recently Issued Accounting Pronouncements

Organization, Basis of Presentation and Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Liabilities Measured at Fair Value on Recurring Basis

Liabilities measured at fair value on a recurring basis are as follows (in thousands):

			Fair Value Measurements at Reporting Date Using:
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
As of December 31, 2018:
Convertible promissory notes	$	1,950	$	—	$	—	$	1,950

As of September 30, 2019:
Warrant liabilities	$	107,373	$	—	$	—	$	107,373
Convertible promissory notes		95,229		—		—		95,229
Total	$	202,602	$	—	$	—	$	202,602

Schedule of Adjustment of Carrying Value to Their Estimated Fair Value

Liability

At initial

valuation

date

Fair value

as of

September 30,

Fair value method

at initial

valuation date

(and relative weighting)

Fair value

method at as of

September 30, 2019 (and

relative weighting)

KEY unobservable inputs

Range

Takeda Warrants

47,894

107,373

Financing transactions (40%)

Income approach (60%)

Financing transactions (70%)

Income approach (30%)

Transaction prices per share

Estimated time to liquidity

Discount rate

$9.33 - $18.56

0.09 - 1.77 years

7.5%

May 2019 Notes

90,250

95,229

Financing transactions (40%)

Income approach (60%)

Financing transactions (70%)

Income approach (30%)

Estimated time to liquidity

Volatility

Discount rate

0.09 - 1.77 years

65%

22.6% - 25%

Schedule of Reconciliation of Liabilities Measured at Fair Value

The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs (in thousands):

	Warrant Liabilities		Convertible Promissory Notes
Balance at January 1, 2018	$	—	$	—
Issuance of convertible promissory notes		—		1,900
Change in fair value		—		50
Balance at December 31, 2018		—		1,950
Issuance of convertible promissory notes		—		90,750
Exchange of convertible promissory notes (Note 4)		—		(2,399	)
Issuance of warrants		48,313		—
Change in fair value		59,060		4,928
Balance at September 30, 2019	$	107,373	$	95,229

Schedule of Potentially Dilutive Securities from Computation of Diluted Net Loss Per Share

The following potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented because their inclusion would have been antidilutive:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Warrants		7,588,000		—		7,588,000		—
Stock options		1,400,528		—		1,400,528		—
Shares subject to repurchase		4,550,428		—		3,342,544		—

Long-Term Debt (Tables)

9 Months Ended

Sep. 30, 2019

Debt Disclosure [Abstract]

Schedule of Long-Term Debt

Long-term debt consists of the following (in thousands):

	September 30, 2019
Long-term debt	$	25,000
Unamortized debt discount		(2,389	)
Long-term debt, net of debt discount	$	22,611

Schedule of Future Minimum Principal and Interest Payments Under Term Loans

Future minimum principal and interest payments under the Term Loans, including the final payment fee, as of September 30, 2019 are as follows (in thousands):

Year ending December 31:
2019	$	458
2020		1,843
2021		6,609
2022		9,533
2023		8,920
2024		5,599
Total principal and interest payments		32,962
Less interest and final payment fee		(7,962	)
Long-term debt	$	25,000

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21506-112644

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21521-112644

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21538-112644

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

Stockholders' Deficit (Tables)

9 Months Ended

Sep. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Unvested Shares

A summary of the Company’s unvested shares is as follows:

Balance at January 1, 2019	—
Vesting restrictions placed on previously issued shares	3,373,408
Sale of unvested common stock	2,524,852
Issuance of unvested restricted stock awards	16,260
Share vesting	(1,458,985	)
Balance at September 30, 2019	4,455,535

Summary of Stock Option Activity

A summary of the Company’s stock option activity and related information is as follows:

	Options Outstanding		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term		Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2018		—
Options granted		1,400,528	$	9.10		—		—
Options exercised and shares vested		—		—		—		—
Options cancelled		—		—		—		—
Balance at September 30, 2019		1,400,528	$	9.10		9.94	$	5,575
Options exercisable as of September 30, 2019		—		—		—		—

Summary of Weighted-Average Assumptions Used to Estimate Fair Value of Stock Options Granted

	Nine Months Ended September 30,
	2019			2018
Assumptions:
Expected term (in years)		6.07			—
Expected volatility		60.17	%		—
Risk free interest rate		1.58	%		—
Dividend yield		—			—

Summary of Stock-Based Compensation Expense

Stock-based compensation expense recognized for all equity awards, including founder stock, has been reported in the combined statements of operations as follows (in thousands):

	Three Months Ended September 30, 2019		Nine Months Ended September 30, 2019
Research and development expense	$	8	$	8
General and administrative expense		29		58
Total	$	37	$	66

Subsequent Events (Tables)

9 Months Ended

Sep. 30, 2019

IPO

Subsequent Event [Line Items]

Summary of Certain Actual and Pro Forma Balance Sheet Data

	September 30, 2019			Pro forma September 30, 2019
Cash and cash equivalents	$	74,484		$	267,164
Prepaid expenses and other current assets		3,169			3,169
Property, plant and equipment, net		40			40
Other assets		2,013			—
Accounts payable and accrued expenses		4,891			1,996
Convertible promissory notes payable		95,229			—
Warrant liabilities		107,373			448
Long-term liabilities		24,674			24,674
Common stock		—			2
Additional paid in capital		5,952			401,665
Accumulated deficit		(158,413	)		(158,413	)
Total stockholder’s (deficit) equity		(152,461	)		243,254

Organization, Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details)			3 Months Ended			4 Months Ended	9 Months Ended		12 Months Ended
	Oct. 29, 2019 USD ($) shares	Oct. 11, 2019 shares	Sep. 30, 2019 USD ($) shares	Jun. 30, 2019 shares	Mar. 31, 2019 shares	May 06, 2019 shares	Sep. 30, 2019 USD ($) Segment shares	Sep. 30, 2018 shares	Dec. 31, 2018 USD ($) $ / shares shares	May 07, 2019 USD ($)	Jun. 30, 2018 shares	Mar. 31, 2018 shares	Dec. 31, 2017 shares
Organization Basis of Presentation and Summary of Significant Accounting Policies [Line Items]
Description of forward stock split							1,559.1183-for-1
Forward stock split conversion ratio									1,559.1183
Common stock, outstanding shares \| shares			7,420,989				7,420,989		6,760,334
Common stock, authorized shares \| shares			50,000,000				50,000,000
Fair value liabilities, level 1 to level 2 transfers, amount			$ 0				$ 0		$ 0
Fair value liabilities, level 2 to level 1 transfers, amount			0				0		0
Fair value liability, transfers into level 3							0		0
Fair value liability, transfers out of level 3							0		0
Deferred offering costs			$ 2,000,000				$ 2,000,000		0
Number of operating segment \| Segment							1
Unvested Shares
Organization Basis of Presentation and Summary of Significant Accounting Policies [Line Items]
Weighted-average unvested shares \| shares			4,550,428				3,342,544	0
Frazier Notes
Organization Basis of Presentation and Summary of Significant Accounting Policies [Line Items]
Fair value of convertible notes									$ 2,000,000
May 2019 Notes
Organization Basis of Presentation and Summary of Significant Accounting Policies [Line Items]
Fair value of convertible notes			$ 95,229,000				$ 95,229,000			$ 90,250,000
Takeda Warrants
Organization Basis of Presentation and Summary of Significant Accounting Policies [Line Items]
Fair value of warrants			107,000,000				107,000,000
Lender Warrants
Organization Basis of Presentation and Summary of Significant Accounting Policies [Line Items]
Fair value of warrants			400,000				400,000
Fair Value, Recurring
Organization Basis of Presentation and Summary of Significant Accounting Policies [Line Items]
Financial assets fair value disclosure			0				0
Fair Value, Nonrecurring
Organization Basis of Presentation and Summary of Significant Accounting Policies [Line Items]
Non-financial assets fair value disclosure			0				0
Non-financial liabilities fair value disclosure			$ 0				$ 0
Subsequent Event
Organization Basis of Presentation and Summary of Significant Accounting Policies [Line Items]
Description of forward stock split		2.168-for-1
Forward stock split conversion ratio		2.168
Common stock, authorized shares \| shares		50,000,000
Common Stock
Organization Basis of Presentation and Summary of Significant Accounting Policies [Line Items]
Common stock shares issued \| shares				1,084,000	1,491,072	2,524,852			1,000
Purchase price \| $ / shares									$ 1.00
Common stock, outstanding shares \| shares			7,420,989	7,219,268	5,932,190		7,420,989	2,000	0		2,000	2,000	0
Common Stock \| YamadaCo
Organization Basis of Presentation and Summary of Significant Accounting Policies [Line Items]
Convertible securities converted into shares of common stock \| shares									1,559.1183
IPO \| Common Stock \| Subsequent Event
Organization Basis of Presentation and Summary of Significant Accounting Policies [Line Items]
Common stock shares issued \| shares	10,997,630
Proceeds from Initial Public Offering (IPO)	$ 191,400,000
Convertible securities converted into shares of common stock \| shares	6,107,918

Organization, Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured at fair value	$ 202,602
Warrant Liabilities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured at fair value	107,373
Convertible Promissory Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured at fair value	95,229	$ 1,950
Significant Unobservable Inputs (Level 3)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured at fair value	202,602
Significant Unobservable Inputs (Level 3) \| Warrant Liabilities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured at fair value	107,373
Significant Unobservable Inputs (Level 3) \| Convertible Promissory Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured at fair value	$ 95,229	$ 1,950

Organization, Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Adjustment of Carrying Value to Their Estimated Fair Value (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)	May 07, 2019 USD ($)
Takeda and Lender Warrants
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of warrant liabilities	$ 107,373	$ 47,894
Takeda Warrants
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of warrant liabilities	$ 107,000
Takeda Warrants \| Income Approach \| Discount Rate
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liabilities, measurement input	7.5
Takeda Warrants \| Minimum \| Financing Transactions
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liabilities, measurement input	9.33
Warrant liabilities, measurement input [Extensible List]	us-gaap:MeasurementInputExercisePriceMember
Takeda Warrants \| Minimum \| Income Approach \| Expected Term
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liabilities, term	1 month 2 days
Takeda Warrants \| Maximum \| Financing Transactions
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liabilities, measurement input	18.56
Warrant liabilities, measurement input [Extensible List]	us-gaap:MeasurementInputExercisePriceMember
Takeda Warrants \| Maximum \| Income Approach \| Expected Term
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liabilities, term	1 year 9 months 7 days
May 2019 Notes
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of convertible promissory notes	$ 95,229	$ 90,250
May 2019 Notes \| Income Approach \| Volatility
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible promissory notes, measurement input	65
May 2019 Notes \| Minimum \| Financing Transactions
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible promissory notes, term	1 month 2 days
Convertible promissory notes, measurement input [Extensible List]	us-gaap:MeasurementInputExpectedTermMember
May 2019 Notes \| Minimum \| Income Approach \| Discount Rate
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible promissory notes, measurement input	22.6
May 2019 Notes \| Maximum \| Financing Transactions
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible promissory notes, term	1 year 9 months 7 days
Convertible promissory notes, measurement input [Extensible List]	us-gaap:MeasurementInputExpectedTermMember
May 2019 Notes \| Maximum \| Income Approach \| Discount Rate
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible promissory notes, measurement input	25

Organization, Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Adjustment of Carrying Value to Their Estimated Fair Value (Parenthetical) (Details)	Sep. 30, 2019	May 07, 2019
Takeda Warrants \| Financing Transactions
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value method, valuation processes percentage	70.00%	40.00%
Takeda Warrants \| Income Approach
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value method, valuation processes percentage	30.00%	60.00%
May 2019 Notes \| Financing Transactions
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value method, valuation processes percentage	70.00%	40.00%
May 2019 Notes \| Income Approach
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value method, valuation processes percentage	30.00%	60.00%

Organization, Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Reconciliation of Liabilities Measured at Fair Value (Details) - Significant Unobservable Inputs (Level 3) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Warrant Liabilities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Issuance of warrants	$ 48,313
Change in fair value	59,060
Ending Balance	107,373
Convertible Promissory Notes
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	1,950
Issuance of convertible promissory notes	90,750	$ 1,900
Exchange of convertible promissory notes (Note 4)	(2,399)
Change in fair value	4,928	50
Ending Balance	$ 95,229	$ 1,950

Organization, Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Warrant
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	7,588,000	7,588,000
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	1,400,528	1,400,528
Shares Subject to Repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	4,550,428	3,342,544

Related Party Transactions - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
Outstanding accounts payable	$ 57,000		$ 57,000		$ 45,000
Frazier
Related Party Transaction [Line Items]
Outstanding accounts payable	71,000		71,000		45,000
Shared operating expenses	200,000	$ 66,000	300,000	$ 200,000
PCI Pharma Services \| Clinical Manufacturing Services
Related Party Transaction [Line Items]
Prepaid services	100,000		100,000
Outstanding accounts payable and accrued expenses	200,000		200,000
Expense related to services	200,000		200,000
Mountain Field LLC
Related Party Transaction [Line Items]
Outstanding accounts receivable	0		0		$ 19,000
Shared operating expenses	$ 0	$ 5,000	$ 100,000	$ 2,000

Commitments and Contingencies - Additional Information (Details) - USD ($)		9 Months Ended
	May 07, 2019	Sep. 30, 2019
Commitments And Contingencies [Line Items]
Common stock, shares issued		11,876,518
Acquired in-process research and development		$ 78,897,000
Takeda License \| Takeda
Commitments And Contingencies [Line Items]
License agreement description		The agreement will remain in effect, on a country-by-country and product-by-product basis, until the later of (i) the expiration of the last to expire valid patent claim covering vonoprazan fumarate alone or in combination with at least one other therapeutically active ingredient, (ii) the expiration of the applicable regulatory exclusivity and (iii) 15 years from the date of first commercial sale, unless earlier terminated. The Company may terminate the Takeda License upon six months’ written notice. The Company and Takeda may terminate the Takeda License in the case of the other party’s insolvency or material uncured breach. Takeda may terminate the Takeda License if the Company challenges, or assists in challenging, licensed patents.
Agreement expiration term from date of first commercial sale	15 years
Cash consideration paid for license	$ 25,000,000
Common stock fair value	$ 5,900,000
Common stock, shares issued	1,084,000
Warrants exercise price	$ 0.00004613
Fair value of warrants	$ 47,900,000
Additional warrant issued	0
Maximum amount payable in sales milestones upon achievement of specified levels of product sales	$ 250,000,000
Transaction costs	$ 100,000
Warrants expiration date	May 07, 2029
Acquired in-process research and development	$ 78,900,000
Takeda License \| Takeda \| Common Stock
Commitments And Contingencies [Line Items]
Warrants issued to purchase shares	7,588,000

Convertible Promissory Notes - Additional Information (Details) - USD ($)			1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 29, 2019	May 07, 2019	Apr. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Frazier Convertible Note Financing
Debt Instrument [Line Items]
Aggregate amount of debt instrument			$ 2,400,000
Debt instrument issued, amount			$ 500,000					$ 1,900,000
Increases (decreases) in fair value of debt instrument					$ 18,000	$ (50,000)	$ 22,000
Interest expense				$ 0	$ 4,000	15,000	$ 8,000
Frazier Convertible Note Financing \| Minimum
Debt Instrument [Line Items]
Debt instrument, interest rate percentage			1.68%
Frazier Convertible Note Financing \| Maximum
Debt Instrument [Line Items]
Debt instrument, interest rate percentage			2.55%
May 2019 Convertible Note Financing
Debt Instrument [Line Items]
Aggregate amount of debt instrument		$ 90,300,000
Debt instrument, interest rate percentage		6.00%
Fair value of convertible promissory notes		$ 2,400,000
Interest expense				1,400,000		2,200,000
Proceeds from issuance of unsecured debt		$ 87,800,000
Debt instrument maturity date		May 07, 2020
Debt instrument due and payable date		May 07, 2022
Debt instrument conversion base amount to calculate to cap price per share		$ 500,000,000
Debt instrument principal amount				90,300,000		90,300,000
Debt instrument accrued interest				2,200,000		2,200,000
May 2019 Convertible Note Financing \| Other Income (Expense)
Debt Instrument [Line Items]
Increases (decreases) in fair value of debt instrument				$ 2,500,000		$ 4,900,000
May 2019 Convertible Note Financing \| Common Stock \| Subsequent Event
Debt Instrument [Line Items]
Debt instrument conversion, shares issued	6,107,918
May 2019 Convertible Note Financing \| Frazier
Debt Instrument [Line Items]
Debt instrument purchased amount		$ 20,000,000
May 2019 Convertible Note Financing \| Minimum
Debt Instrument [Line Items]
Minimum percentage of outstanding principal payable at maturity date		60.00%
May 2019 Convertible Note Financing \| Maximum
Debt Instrument [Line Items]
Qualified equity financing conversion price percentage per share		80.00%
Non-qualified equity financing conversion price percentage per share		80.00%
Initial public offering conversion price percentage per share		80.00%

Long-Term Debt - Schedule of Long-Term Debt (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Debt Disclosure [Abstract]
Long-term debt	$ 25,000
Unamortized debt discount	(2,389)
Long-term debt, net of debt discount	$ 22,611

Long-Term Debt - Additional Information (Details) - USD ($)		3 Months Ended	6 Months Ended	9 Months Ended
	May 14, 2019	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2019
Debt Instrument [Line Items]
Long-term debt		$ 25,000,000	$ 25,000,000	$ 25,000,000
Loan Agreement
Debt Instrument [Line Items]
Interest bearing rate upon customary events	4.00%
Warrants expire term	10 years
Warrants earlier termination date	Sep. 30, 2020
Aggregate repurchase price of warrants	$ 500,000
Fair value of warrant liabilities	400,000
Interest expense		$ 600,000		$ 900,000
Term Loans
Debt Instrument [Line Items]
Aggregate amount of debt instrument	25,000,000
Debt instrument, additional borrowing capacity amount	$ 25,000,000
Debt instrument, covenant description				Term Loan B is available through March 31, 2020, provided that (i) the Company has received at least $150.0 million of net cash proceeds in connection with the issuance and sale, subsequent to April 1 2019, of its equity securities and subordinated debt, (ii) the Company has initiated Phase 3 clinical trials for vonoprazan, and (iii) no event of default has occurred.
Debt instrument, interest rate percentage		7.25%	7.25%	7.25%
Debt instrument, description				The monthly payments consist of interest-only through June 1, 2021 or, in the event of positive data with respect to the Company’s Phase 3 clinical trial in both indications for vonoprazan sufficient to file an NDA with the FDA, through June 1, 2022.
Debt instrument maturity date	May 01, 2024
Debt instrument, final payment fee percentage	8.25%
Debt instrument, final payment fee		$ 2,100,000	$ 2,100,000	$ 2,100,000
Debt issuance costs	$ 200,000
Long-term debt		25,000,000	25,000,000	25,000,000
Accrued interest		$ 200,000	200,000	$ 200,000
Term Loans \| Prime Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.75%
Term Loans \| Minimum
Debt Instrument [Line Items]
Threshold proceeds from issuance of equity securities and subordinated debt to borrow additional debt			$ 150,000,000
Term Loans \| Maximum
Debt Instrument [Line Items]
Debt instrument, prepayment fee percentage of outstanding principal amount	2.00%

Long-Term Debt - Schedule of Future Minimum Principal and Interest Payments Under Term Loans (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Debt Disclosure [Abstract]
2019	$ 458
2020	1,843
2021	6,609
2022	9,533
2023	8,920
2024	5,599
Total principal and interest payments	32,962
Less interest and final payment fee	(7,962)
Long-term debt	$ 25,000

Stockholders' Deficit - Additional Information (Details) - USD ($)		1 Months Ended		3 Months Ended			4 Months Ended	9 Months Ended		12 Months Ended
	Oct. 29, 2019	May 31, 2019	Mar. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	May 06, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Oct. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from issuance of common stock									$ 2,000
Unvested stock				4,455,535				4,455,535
Stock options, granted								1,400,528
Unrecognized stock-based compensation expense				$ 3,800,000				$ 3,800,000
Unrecognized stock-based compensation expense, weighted-average period for recognition								3 years 8 months 19 days
Stock-based compensation expense				37,000				$ 66,000	$ 0
Employee and Nonemployee Director
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Estimated weighted-average fair value								$ 5.12
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation arrangement by share based payment award, vested fair value				$ 37,000				$ 66,000
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield								0.00%
Existing Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares authorized for issuance				2,231,739				2,231,739
Common stock, shares available for grant				814,951				814,951
Vesting of restricted shares (unaudited), shares		16,260
Stock options, granted								1,400,258
Existing Incentive Plan \| Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested stock				6,775				6,775
Stock awards, granted								16,260
Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued					1,084,000	1,491,072	2,524,852			1,000
Number of shares authorized to repurchase			3,373,408			3,373,408
Stock repurchase program, number of shares right lapse			843,352			843,352
Remaining number of shares to be repurchased			2,530,056	2,213,808		2,530,056		2,213,808
Stock repurchase program, period in force			48 months
Stock repurchase program expiration date			Mar. 31, 2023
Proceeds from issuance of common stock							$ 1,000,000
Repurchase right lapse each month after first anniversary, shares							0.000208
Vesting of restricted shares (unaudited), shares				201,721	203,078	1,054,192
Common Stock \| Subsequent Event \| Existing Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares authorized for issuance											2,700,000
Common Stock \| IPO \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued	10,997,630
Proceeds from Initial Public Offering (IPO)	$ 191,400,000
Common Stock \| First Anniversary
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Repurchase right lapse rate							25.00%
Common Stock \| Takeda License
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued		1,084,000
Common Stock \| Frazier
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued			1,491,072

Stockholders' Deficit - Summary of Unvested Shares (Details)	9 Months Ended
	Sep. 30, 2019 shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Vesting restrictions placed on previously issued shares	3,373,408
Sale of unvested common stock	2,524,852
Issuance of unvested restricted stock awards	16,260
Share vesting	(1,458,985)
Balance at September 30, 2019	4,455,535

Stockholders' Deficit - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Options granted	1,400,528
Options Outstanding, Ending Balance	1,400,528
Weighted-Average Exercise Price, Options granted	$ 9.10
Weighted-Average Exercise Price, Ending Balance	$ 9.10
Weighted-Average Remaining Contractual Term	9 years 11 months 8 days	0 years
Weighted-Average Remaining Contractual Term, Options exercisable	0 years
Aggregate Intrinsic Value, Balance	$ 5,575

Stockholders' Deficit - Summary of Weighted-Average Assumptions Used to Estimate Fair Value of Stock Options Granted (Details)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Assumptions:
Expected term (in years)	6 years 25 days	0 years
Expected volatility	60.17%
Risk free interest rate	1.58%

Stockholders' Deficit - Summary of Stock-Based Compensation Expense (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 37,000	$ 66,000	$ 0
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	8,000	8,000
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 29,000	$ 58,000

Subsequent Events - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		4 Months Ended	9 Months Ended	12 Months Ended
	Oct. 29, 2019	Oct. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	May 06, 2019	Sep. 30, 2019	Dec. 31, 2018	Oct. 11, 2019
Subsequent Event [Line Items]
Common stock, authorized shares						50,000,000
Payment of offering costs						$ 1,299
Existing Incentive Plan
Subsequent Event [Line Items]
Number of shares available for grant						2,231,739
Common Stock
Subsequent Event [Line Items]
Shares issued			1,084,000	1,491,072	2,524,852		1,000
Subsequent Event
Subsequent Event [Line Items]
Common stock, authorized shares								50,000,000
Subsequent Event \| Existing Incentive Plan
Subsequent Event [Line Items]
Annual increase to shares available for issuance percentage of outstanding common stock		5.00%
Equity plan, description		The number of shares initially available for issuance will be increased by (i) the number of shares subject to stock options or similar awards granted under the Existing Incentive Plan that expire or otherwise terminate without having been exercised in full after the effective date of the 2019 Plan and unvested shares issued pursuant to awards granted under the Existing Incentive Plan that are forfeited to or repurchased by the Company after the effective date of the 2019 Plan, with the maximum number of shares to be added to the 2019 Plan pursuant to clause (i) above equal to 1,416,788 shares, and (ii) an annual increase on January 1 of each calendar year beginning in 2020 and ending in 2029, equal to the lesser of (a) 5% of the shares of common stock outstanding on the final day of the immediately preceding calendar year and (b) such smaller number of shares as determined by the board of directors.
Subsequent Event \| Employee Stock Purchase Plan
Subsequent Event [Line Items]
Annual increase to shares available for issuance percentage of outstanding common stock		1.00%
Equity plan, description		In addition, the number of shares available for issuance under the ESPP will be annually increased on January 1 of each calendar year beginning in 2020 and ending in 2029, by an amount equal to the lesser of: (i) 1% of the shares outstanding on the final day of the immediately preceding calendar year and (ii) such smaller number of shares as is determined by the board of directors.
Common stock initially reserved for issuance		270,000
Subsequent Event \| Common Stock \| Existing Incentive Plan
Subsequent Event [Line Items]
Number of shares available for grant		2,700,000
Additional number of shares available for issuance		1,416,788
Subsequent Event \| Common Stock \| Employee Stock Purchase Plan
Subsequent Event [Line Items]
Maximum percentage of eligible compensation contributed by participants		20.00%
Subsequent Event \| Common Stock \| Convertible Notes Payable
Subsequent Event [Line Items]
Conversion of notes, common stock shares issued	6,107,918
Subsequent Event \| IPO \| Common Stock
Subsequent Event [Line Items]
Shares issued	10,997,630
Common stock, price per share	$ 19.00
Proceeds from Initial Public Offering (IPO)	$ 191,400
Payment of offering costs	$ 17,600

Subsequent Events - Summary of Certain Actual and Pro Forma Balance Sheet Data (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Cash and cash equivalents	$ 74,484			$ 879
Prepaid expenses and other current assets (including related party amounts of $36 and $19, respectively)	3,169			23
Property, plant and equipment, net	40
Other assets	2,013
Convertible promissory notes payable at fair value (including related party amounts of $21,103 and $1,950, respectively)	95,229			1,950
Warrant liabilities (including related party amounts of ($106,925 and $0, respectively)	107,373
Additional paid-in capital	5,952			2
Accumulated deficit	(158,413)			(1,288)
Total stockholder’s (deficit) equity	(152,461)	$ (84,385)	$ (2,537)	$ (1,286)	$ (802)	$ (512)	$ (252)	$ 0
IPO
Subsequent Event [Line Items]
Cash and cash equivalents	74,484
Prepaid expenses and other current assets (including related party amounts of $36 and $19, respectively)	3,169
Property, plant and equipment, net	40
Other assets	2,013
Accounts payable and accrued expenses	4,891
Convertible promissory notes payable at fair value (including related party amounts of $21,103 and $1,950, respectively)	95,229
Warrant liabilities (including related party amounts of ($106,925 and $0, respectively)	107,373
Long-term liabilities	24,674
Additional paid-in capital	5,952
Accumulated deficit	(158,413)
Total stockholder’s (deficit) equity	(152,461)
IPO \| Pro Forma
Subsequent Event [Line Items]
Cash and cash equivalents	267,164
Prepaid expenses and other current assets (including related party amounts of $36 and $19, respectively)	3,169
Property, plant and equipment, net	40
Accounts payable and accrued expenses	1,996
Warrant liabilities (including related party amounts of ($106,925 and $0, respectively)	448
Long-term liabilities	24,674
Common stock	2
Additional paid-in capital	401,665
Accumulated deficit	(158,413)
Total stockholder’s (deficit) equity	$ 243,254