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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2019	Jul. 31, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	EVOK
Entity Registrant Name	Evoke Pharma Inc
Entity Central Index Key	0001403708
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		24,113,956
Entity File Number	001-36075
Entity Tax Identification Number	208447886
Entity Address, Address Line One	420 Stevens Avenue
Entity Address, Address Line Two	Suite 370
Entity Address, City or Town	Solana Beach
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92075
City Area Code	(858)
Local Phone Number	345-1494

Condensed Balance Sheets (Unaudited) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Current Assets:
Cash and cash equivalents	$ 7,440,079	$ 5,319,004
Prepaid expenses	109,739	329,218
Other current assets	11,551
Total current assets	7,561,369	5,648,222
Operating lease right-of-use asset	69,795
Other assets		11,551
Total assets	7,631,164	5,659,773
Current Liabilities:
Accounts payable and accrued expenses	407,517	476,202
Accrued compensation	807,706	1,158,251
Operating lease liability	69,795
Total current liabilities	1,285,018	1,634,453
Stockholders' equity:
Common stock, $0.0001 par value; authorized shares - 50,000,000; issued and outstanding shares - 24,113,956 and 17,427,533 at June 30, 2019 and December 31, 2018, respectively	2,411	1,743
Additional paid-in capital	89,027,832	82,628,312
Accumulated deficit	(82,684,097)	(78,604,735)
Total stockholders' equity	6,346,146	4,025,320
Total liabilities and stockholders' equity	$ 7,631,164	$ 5,659,773

Condensed Statements of Operations (Unaudited) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating expenses:
Research and development	$ 1,205,599	$ 1,388,791	$ 1,952,481	$ 2,774,157
General and administrative	918,139	917,305	2,141,152	1,949,550
Total operating expenses	2,123,738	2,306,096	4,093,633	4,723,707
Loss from operations	(2,123,738)	(2,306,096)	(4,093,633)	(4,723,707)
Other income:
Interest income	9,642	2,902	14,271	4,335
Gain from change in fair value of warrant liability				433,392
Total other income	9,642	2,902	14,271	437,727
Net loss	$ (2,114,096)	$ (2,303,194)	$ (4,079,362)	$ (4,285,980)
Net loss per share of common stock, basic and diluted	$ (0.09)	$ (0.14)	$ (0.20)	$ (0.27)
Weighted-average shares used to compute basic and diluted net loss per share	23,258,567	16,425,468	20,371,442	15,926,253

Condensed Statements of Stockholders' Equity (Unaudited) - USD ($)	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]
Beginning Balance at Dec. 31, 2017	$ 2,165,749	$ 1,541	$ 73,202,863	$ (71,038,655)
Beginning Balance, Shares at Dec. 31, 2017		15,413,610
Stock-based compensation expense	393,775		393,775
Issuance of common stock, net	544,643	$ 27	544,616
Issuance of common stock, shares net		268,870
Reclassification of warrant liability due to warrant amendment	3,267,885		3,267,885
Net loss	(1,982,786)			(1,982,786)
Ending Balance at Mar. 31, 2018	4,389,266	$ 1,568	77,409,139	(73,021,441)
Ending Balance, Shares at Mar. 31, 2018		15,682,480
Beginning Balance at Dec. 31, 2017	2,165,749	$ 1,541	73,202,863	(71,038,655)
Beginning Balance, Shares at Dec. 31, 2017		15,413,610
Net loss	(4,285,980)
Ending Balance at Jun. 30, 2018	5,360,378	$ 1,690	80,683,323	(75,324,635)
Ending Balance, Shares at Jun. 30, 2018		16,898,664
Beginning Balance at Mar. 31, 2018	4,389,266	$ 1,568	77,409,139	(73,021,441)
Beginning Balance, Shares at Mar. 31, 2018		15,682,480
Stock-based compensation expense	387,429		387,429
Issuance of common stock, net	2,886,877	$ 122	2,886,755
Issuance of common stock, shares net		1,216,184
Net loss	(2,303,194)			(2,303,194)
Ending Balance at Jun. 30, 2018	5,360,378	$ 1,690	80,683,323	(75,324,635)
Ending Balance, Shares at Jun. 30, 2018		16,898,664
Beginning Balance at Dec. 31, 2018	$ 4,025,320	$ 1,743	82,628,312	(78,604,735)
Beginning Balance, Shares at Dec. 31, 2018	17,427,533	17,427,533
Stock-based compensation expense	$ 378,959		378,959
Issuance of common stock, net	636,432	$ 45	636,387
Issuance of common stock, shares net		450,000
Net loss	(1,965,266)			(1,965,266)
Ending Balance at Mar. 31, 2019	3,075,445	$ 1,788	83,643,658	(80,570,001)
Ending Balance, Shares at Mar. 31, 2019		17,877,533
Beginning Balance at Dec. 31, 2018	$ 4,025,320	$ 1,743	82,628,312	(78,604,735)
Beginning Balance, Shares at Dec. 31, 2018	17,427,533	17,427,533
Net loss	$ (4,079,362)
Ending Balance at Jun. 30, 2019	$ 6,346,146	$ 2,411	89,027,832	(82,684,097)
Ending Balance, Shares at Jun. 30, 2019	24,113,956	24,113,956
Beginning Balance at Mar. 31, 2019	$ 3,075,445	$ 1,788	83,643,658	(80,570,001)
Beginning Balance, Shares at Mar. 31, 2019		17,877,533
Stock-based compensation expense	344,841		344,841
Issuance of common stock, net	5,039,956	$ 623	5,039,333
Issuance of common stock, shares net		6,236,423
Net loss	(2,114,096)			(2,114,096)
Ending Balance at Jun. 30, 2019	$ 6,346,146	$ 2,411	$ 89,027,832	$ (82,684,097)
Ending Balance, Shares at Jun. 30, 2019	24,113,956	24,113,956

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Condensed Statements of Cash Flows (Unaudited) - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities
Net loss	$ (4,079,362)	$ (4,285,980)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	723,800	781,204
Change in fair value of warrant liability		(433,392)
Change in operating assets and liabilities:
Prepaid expenses and other assets	285,496	167,364
Accounts payable and other current liabilities	(485,247)	(808,904)
Net cash used in operating activities	(3,555,313)	(4,579,708)
Financing activities
Proceeds from issuance of common stock, net	5,676,388	3,431,520
Net cash provided by financing activities	5,676,388	3,431,520
Net increase (decrease) in cash and cash equivalents	2,121,075	(1,148,188)
Cash and cash equivalents at beginning of period	5,319,004	7,679,267
Cash and cash equivalents at end of period	$ 7,440,079	6,531,079
Non-cash financing activities
Reclassification of warrant liability to equity due to amendment of warrants		$ 3,267,885

Organization and Basis of Presentation

6 Months Ended

Jun. 30, 2019

Organization And Basis Of Presentation [Abstract]

Organization and Basis of Presentation

1. Organization and Basis of Presentation

Evoke Pharma, Inc. (the “Company”) was incorporated in the state of Delaware in January 2007. The Company is a specialty pharmaceutical company focused primarily on the development of drugs to treat gastroenterological disorders and disease.

Since its inception, the Company has devoted substantially all of its efforts to developing its sole product candidate, Gimoti™, and has not realized revenues from its planned principal operations. The Company filed a 505(b)(2) New Drug Application (“NDA”) for Gimoti with the U.S. Food and Drug Administration (“FDA”) on June 1, 2018, and on April 1, 2019, the Company received a Complete Response Letter (“CRL”) from FDA for the NDA. The CRL stated that FDA has determined it cannot approve the NDA in its present form and provided recommendations to address the two remaining approvability issues in an NDA resubmission. The approvability issues are related to clinical pharmacology and product quality/device quality. FDA did not request any new clinical data and did not raise any safety concerns.

On July 25, 2019, the Company completed a type A meeting with FDA to obtain FDA’s feedback and agreement on the Company’s plan to address deficiencies cited in the CRL in support of a resubmission of the Gimoti NDA. The focus of the discussion was on topics noted in the CRL, including the root cause analysis of low drug exposure in the comparative bioavailability study and additional product quality/device quality control testing.

Based on FDA feedback and the meeting minutes, the Company will include its root cause analysis and previously collected patient use and experience information in its resubmission package. The Company also agreed to provide an analysis of pump performance characteristics on the nasal spray devices used in the comparative bioavailability study and 3-month stability data from commercial scale batches of Gimoti which the Company initiated manufacturing in June 2019. No additional human clinical trials were requested by FDA and the Company plans to resubmit the Gimoti NDA in the fourth quarter of 2019.

The Company does not anticipate realizing revenues until FDA approves the NDA and the Company begins commercializing Gimoti, which events may never occur. The Company’s activities are subject to the significant risks and uncertainties associated with any specialty pharmaceutical company that has substantial expenditures for research and development, including funding its operations.

Going Concern

The Company has incurred recurring losses and negative cash flows from operations since inception and expects to continue to incur net losses for the foreseeable future until such time, if ever, that it can generate significant revenues from the sale of Gimoti. Although the Company ended the second quarter of 2019 with approximately $7.4 million in cash and cash equivalents, the Company anticipates that it will continue to incur losses from operations due to pre-approval and pre-commercialization activities, including interactions with FDA on the Company’s NDA submission for Gimoti, responding to approvability issues raised in the CRL received from FDA, manufacturing of registration, and potentially commercial batches of Gimoti, and general and administrative costs to support operations. As a result, the Company believes that there is substantial doubt about its ability to continue as a going concern for one year after the date these financial statements are issued.

The determination as to whether the Company can continue as a going concern contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. In its report on the Company’s financial statements for the year ended December 31, 2018, the Company’s independent registered public accounting firm included an explanatory paragraph expressing substantial doubt regarding the Company’s ability to continue as a going concern.

The Company’s net losses may fluctuate significantly from quarter to quarter and year to year. The Company believes, based on its current operating plan, that its existing cash and cash equivalents will be sufficient to fund its operations into the second quarter of 2020. If Gimoti is approved by FDA, additional funds will become available from the Novos Growth, LLC (“NGP”) Working Capital Loan and the NGP Credit Agreement, as disclosed in Note 6. Under either situation, the Company will be required to raise additional funds through debt, equity or other forms of financing, such as potential collaboration arrangements, to fund future operations and continue as a going concern.

There can be no assurance that additional financing will be available when needed or on acceptable terms. If the Company is not able to secure adequate additional funding, the Company may be forced to make reductions in spending, extend payment terms with suppliers, and/or suspend or curtail planned programs. Any of these actions could materially harm the Company’s business, results of operations, financial condition and future prospects. There can be no assurance that the Company will be able to further develop Gimoti, if required, and resubmit and receive FDA approval of the Gimoti NDA. Because the Company’s business is entirely dependent on the success of Gimoti, if the Company is unable to secure additional financing or identify and execute on other development or strategic alternatives for Gimoti or our company, the Company will be required to curtail all of its activities and may be required to liquidate, dissolve or otherwise wind down its operations.

Notice of Delisting

On May 15, 2019, the Company received a letter from Nasdaq indicating that, for the last thirty consecutive business days, the bid price for the Company’s common stock had closed below the minimum $1.00 per share requirement for continued listing on The Nasdaq Capital Market.

In accordance with Nasdaq listing rules, the Company has been provided an initial period of 180 calendar days, or until November 11, 2019, to regain compliance. The letter states that Nasdaq will provide written notification that the Company has achieved compliance with its rules if at any time before November 11, 2019, the bid price of the Company’s common stock closes at $1.00 per share or more for a minimum of ten consecutive business days. The Nasdaq letter has no immediate effect on the listing or trading of the Company’s common stock and the common stock will continue to trade on The Nasdaq Capital Market.

The Company intends to monitor the bid price of its common stock and consider available options if its common stock does not trade at a level likely to result in the Company regaining compliance with Nasdaq’s minimum bid price rule by November 11, 2019.

If the Company does not regain compliance with Nasdaq listing rules by November 11, 2019, the Company may be eligible for an additional 180 calendar day compliance period. To qualify, the Company would be required to meet the continued listing requirement for market value of publicly held shares and all other initial listing standards for The Nasdaq Capital Market, with the exception of the bid price requirement, and would need to provide written notice of its intention to cure the deficiency during the second compliance period, by effecting a reverse stock split, if necessary. However, if it appears to Nasdaq that the Company will not be able to cure the deficiency, or if the Company is otherwise not eligible, Nasdaq would notify the Company that its securities would be subject to delisting. In the event of such a notification, the Company may appeal Nasdaq’s determination to delist its securities, but there can be no assurance Nasdaq would grant the Company’s request for continued listing.

Summary of Significant Accounting Policies

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

The accompanying condensed balance sheet as of December 31, 2018, which has been derived from audited financial statements, and the unaudited interim condensed financial statements, have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) and follow the requirements of the U.S. Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by GAAP can be condensed or omitted. In management’s opinion, the unaudited interim financial statements have been prepared on the same basis as the audited financial statements and include all adjustments, which include only normal recurring adjustments, necessary for the fair presentation of the Company’s financial position and its results of operations and its cash flows for the periods presented. These statements do not include all disclosures required by GAAP and should be read in conjunction with the Company’s financial statements and accompanying notes for the year ended December 31, 2018, which are contained in the Company’s Annual Report on Form 10-K filed with the SEC on March 6, 2019. The results for interim periods are not necessarily indicative of the results expected for the full fiscal year or any other interim period.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ materially from those estimates.

Contract Research Organizations and Consultants

The Company relies on contract research organizations (“CROs”) and consultants to assist with ongoing regulatory discussions and submissions supporting the NDA. If these CROs and consultants are unable to continue their support, this could adversely affect FDA’s review of the NDA.

In addition, the Company relies on third-party manufacturers for the production of Gimoti. If the third-party manufacturers are unable to continue manufacturing Gimoti, or if the Company loses one of its sole source suppliers used in its manufacturing processes, the Company may not be able to meet any development needs or commercial supply demand for Gimoti, if approved by FDA, and the development and/or commercialization of Gimoti could be materially and adversely affected.

The Company also relies on third-party sales and marketing organizations for the management of the pre-commercial launch preparation for Gimoti, as well as for a dedicated sales team to sell Gimoti, if approved by FDA. If such third-party organizations are unable to continue managing the launch preparation, or serving as a dedicated sales team, the commercialization of Gimoti could be materially and adversely affected.

Warrant Accounting

In March 2018, the Company entered into warrant amendments (the “Warrant Amendments”) with each of the holders of the Company’s outstanding warrants to purchase common stock issued on July 25, 2016 and August 3, 2016 (the “Warrants”). As a result of the Warrant Amendments, the Warrants are no longer classified as a liability on the Company’s balance sheet, were adjusted to fair value as of the date of the Warrant Amendments, and were reclassified to additional paid-in capital, a component of stockholders’ equity.

Prior to the Warrant Amendments, the Warrants were classified as warrant liability and recorded at fair value. These Warrants contained a feature that could have required the transfer of cash in the event a change of control occurred without the authorization of our board of directors, and therefore, were classified as a liability in accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification 480, Distinguishing Liabilities from Equity.

This warrant liability was subject to remeasurement at each reporting date and the Company recognized any change in the fair value of the warrant liability in the statement of operations. The Company continued to adjust the carrying value of the warrants for changes in the estimated fair value until the date of the Warrant Amendments.

Stock-Based Compensation

Stock-based compensation expense for stock option grants and employee stock purchases under the Company’s Employee Stock Purchase Plan (the “ESPP”) is recorded at the estimated fair value of the award as of the grant date and is recognized as expense on a straight-line basis over the employee’s requisite service period. The estimation of stock option and ESPP fair value requires management to make estimates and judgments about, among other things, employee exercise behavior, forfeiture rates and volatility of the Company’s common stock. The judgments directly affect the amount of compensation expense that will be recognized.

The Company grants stock options to purchase common stock to employees and members of the board of directors with exercise prices equal to the Company’s closing market price on the date the stock options are granted. The risk-free interest rate assumption was based on the yield of an applicable rate for U.S. Treasury instruments with maturities similar to those of the expected term of the award being valued. The weighted-average expected term of options and employee stock purchases was calculated using the simplified method as prescribed by accounting guidance for stock-based compensation. This decision was based on the lack of relevant historical data due to the Company’s limited historical experience. In addition, due to the Company’s limited historical data, the estimated volatility was calculated based upon the Company’s historical volatility and, if necessary, supplemented with historical volatility of comparable companies in the biotechnology industry whose share prices are publicly available for a sufficient period of time. The assumed dividend yield was based on the Company never paying cash dividends and having no expectation of paying cash dividends in the foreseeable future.

Research and Development Expenses

Research and development costs are expensed as incurred and primarily include compensation and related benefits, stock-based compensation expense and costs paid to third-party contractors for product development activities and drug product materials. The Company expenses costs relating to the purchase and production of pre-approval inventories as research and development expense in the period incurred until FDA approval is received.

The Company does not own or operate manufacturing facilities for the production of Gimoti, nor does it plan to develop its own manufacturing operations in the foreseeable future. The Company currently depends on third-party contract manufacturers for all of its required raw materials, drug substance and finished product for its pre-commercial product development. The Company has agreements with Cosma S.p.A. to supply metoclopramide for the manufacture of Gimoti, and with Thermo Fisher Scientific Inc., who acquired Patheon UK Limited, for product development and manufacturing of Gimoti. The Company currently utilizes third-party consultants, which it engages on an as-needed, hourly basis, to manage product development and manufacturing contractors.

Net Loss Per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average number of common stock outstanding for the period, without consideration for common stock equivalents and adjusted for the weighted-average number of common stock outstanding that are subject to repurchase. The Company excluded 30,165 and 37,582 shares of common stock subject to repurchase from the weighted-average number of common stock outstanding for the three and six months ended June 30, 2018, respectively. Since the Company’s repurchase right lapsed upon the filing of the NDA in June 2018, the Company no longer has any common stock subject to repurchase. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common stock equivalents outstanding for the period determined using the treasury-stock method. Dilutive common stock equivalents are comprised of common stock subject to repurchase, warrants to purchase common stock, options to purchase common stock under the Company’s equity incentive plans and potential shares to be purchased under the ESPP. For the periods presented, the following table sets forth the outstanding potentially dilutive securities that have been excluded from the calculation of diluted net loss per share because their inclusion would be anti-dilutive:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Common stock subject to repurchase	—			30,165	—			37,582
Warrants to purchase common stock		2,713,561		2,797,561		2,713,561		2,797,561
Common stock options		3,232,871		3,017,624		3,232,871		3,017,624
Employee stock purchase plan	—			19,144	—			26,047
Total excluded securities		5,946,432		5,864,494		5,946,432		5,878,814

Recent Accounting Pronouncements

In February 2016, the FASB issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842). The new standard establishes a right-of-use (“ROU”) model that requires a lessee to record a ROU asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. The Company adopted this standard effective January 1, 2019, as required. The Company determines if an arrangement is a finance lease, operating lease or short-term lease at inception. The Company elected the “package of practical expedients,” which permits the Company not to reassess prior conclusions about lease identifications, lease classification and initial direct costs. The Company also elected not to separate lease and non-lease components when certain conditions are met. As discussed in Note 3, the Company’s only significant lease is its facility lease, which expires on December 31, 2019, and is classified as an operating lease.

Stockholders' Equity

6 Months Ended

Jun. 30, 2019

Equity [Abstract]

Stockholders' Equity

5. Stockholders’ Equity

At the Market Equity Offering Program

In November 2017, the Company filed a shelf registration with the SEC on Form S-3. The shelf registration statement includes a prospectus for the at-the-market offering to sell up to an aggregate of $16.0 million of shares of the Company’s common stock through B. Riley FBR, Inc. (“FBR”) as a sales agent (the “FBR Sales Agreement”). During the six months ended June 30, 2018, the Company sold 1,485,054 shares of common stock at a weighted-average price per share of $2.38 pursuant to the FBR Sales Agreement and received proceeds of approximately $3.4 million, net of commissions and fees. During the six months ended June 30, 2019, the Company sold 6,686,423 shares of common stock at a weighted-average price per share of $0.87 pursuant to the FBR Sales Agreement and received proceeds of approximately $5.7 million, net of commissions and fees.

Future sales will depend on a variety of factors including, but not limited to, market conditions, the trading price of the Company’s common stock and the Company’s capital needs. There can be no assurance that FBR will be successful in consummating future sales based on prevailing market conditions or in the quantities or at the prices that the Company deems appropriate.

In addition, the Company will not be able to make future sales of common stock pursuant to the FBR Sales Agreement unless certain conditions are met, which include the accuracy of representations and warranties made to FBR under the FBR Sales Agreement. Furthermore, FBR is permitted to terminate the FBR Sales Agreement in its sole discretion upon ten days’ notice, or at any time in certain circumstances, including the occurrence of an event that would be reasonably likely to have a material adverse effect on the Company’s assets, business, operations, earnings, properties, condition (financial or otherwise), prospects, stockholders’ equity or results of operations. The Company has no obligation to sell the remaining shares available for sale pursuant to the FBR Sales Agreement.

Warrants

In March 2018, the Company entered into the Warrant Amendments with each of the holders of the Company’s outstanding Warrants acquired as a part of the Company’s financings which closed in July and August 2016. As a result of the Warrant Amendments, all of the remaining Warrants to purchase 2,449,129 shares of the Company’s common stock are no longer required to be classified as liabilities. The value of the amended Warrants was adjusted to the fair value immediately prior to the Warrant Amendments, resulting in a net gain of approximately $433,000 in the statement of operations, and approximately $3.3 million was reclassified from warrant liability to additional paid-in capital.

In September 2018, warrants to purchase 84,000 shares of the Company’s common stock, issued to representatives of the underwriters in connection with the Company’s initial public offering in September 2013, expired and were cancelled.

Stock-Based Compensation

Stock-based compensation expense includes charges related to employee stock purchases under the ESPP and stock option grants. The Company measures stock-based compensation expense based on the grant date fair value of any awards granted to its employees. Such expense is recognized over the period of time that employees provide service and earn rights to the awards.

In June 2019, the Company effected a one-time option exchange, wherein employees were offered the opportunity to exchange certain outstanding stock options for the grant of a lesser number of replacement stock options. The participants received three new stock options for every four stock options tendered for exchange. As a result, 2,456,999 stock options were exchanged for 1,842,746 replacement stock options. The replacement stock options have a four-year vesting schedule and an exercise price of $0.62 per share, which was the closing price of the Company’s common stock on the date of the option exchange. All other terms of the replacement stock options remain the same as the original stock options that were exchanged. As a result of this transaction, the Company will recognize approximately $84,000 of additional stock-based compensation expense over the four-year vesting term of the exchanged options.

The estimated fair value of each stock option award granted was determined on the date of grant using the Black Scholes option-pricing valuation model with the following weighted-average assumptions for option grants during the three and six months ended June 30, 2019 and 2018:

	Three Months Ended June 30,		Six Months Ended June 30,
	2019	2018	2019	2018
Common Stock Options
Risk free interest rate	1.80%-2.36%	2.85%	1.80%-2.55%	2.66%-2.85%
Expected option term	4.27-5.77 years	5.5 years	4.27-6.0 years	5.5-6.0 years
Expected volatility of common stock	101.46%-112.58%	92.30%	90.34%-112.58%	90.15%-92.30%
Expected dividend yield	0.0%	0.0%	0.0%	0.0%

The estimated fair value of the shares to be acquired under the ESPP was determined on the initiation date of each six-month purchase period using the Black-Scholes option-pricing valuation model with the following weighted-average assumptions for ESPP shares to be purchased during the six months ended June 30, 2019 and 2018:

	Six Months Ended June 30,
	2019	2018
Employee Stock Purchase Plan
Risk free interest rate	2.52%	1.85%
Expected term	0.5 years	0.5 years
Expected volatility of common stock	130.36%	58.76%
Expected dividend yield	0.0%	0.0%

The Company recognized non-cash stock-based compensation expense to employees and directors in its research and development and its general and administrative functions as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development	$	202,117	$	168,733	$	354,291	$	357,510
General and administrative		142,724		218,696		369,509		423,694
Total stock-based compensation expense	$	344,841	$	387,429	$	723,800	$	781,204

As of June 30, 2019, there were approximately $2.7 million of unrecognized compensation costs related to outstanding employee and board of director options, which are expected to be recognized over a weighted-average period of 1.4 years.

Commercial Services Agreement

6 Months Ended

Jun. 30, 2019

Commercial Services Agreement [Abstract]

Commercial Services Agreement

6. Commercial Services Agreement

On January 5, 2019, the Company entered into a commercial services agreement with NGP (the “NGP Agreement”) for the commercialization of Gimoti. Pursuant to the NGP Agreement, NGP will manage the commercial operations for a dedicated sales team to market Gimoti, if approved by FDA, to gastroenterologists and other targeted health care providers.

Under the terms of the NGP Agreement, the Company maintains ownership of the Gimoti NDA, as well as legal, regulatory, and manufacturing responsibilities for Gimoti. The Company will also retain a contract sales organization, which would be managed by NGP. The Company will record sales for Gimoti and retain more than 80% of product profits. NGP will receive a percentage of product profits in the mid-to-high teens as a service fee (such product profit amount, the “Contribution Profits”).

Pursuant to the NGP Agreement, upon any Gimoti NDA approval, NGP has agreed to finance the Company’s working capital requirements for specified commercialization costs in an amount by which Contribution Profits are expected to fall (or do actually fall) below zero (as projected by sales forecasts and a commercialization budget) to be drawn by the Company on a monthly basis, as needed (“NGP Working Capital Loan”), pursuant to a credit agreement to be negotiated in good faith between the Company and NGP (“NGP Credit Agreement”). The NGP Working Capital Loan will be repaid by the Company, if at all, only out of positive Contribution Profits, unless the NGP Agreement is terminated (a) by NGP due to a material breach by the Company, or (b) by the Company other than due to the gross negligence or intentional misconduct of NGP. Termination of the NGP Agreement by NGP for any other reason (including, without limitation, minimum net sales thresholds and negative Contribution Profits, as described below) will cause the NGP Working Capital Loan to be forgiven in full. The interest rate and other terms of the NGP Working Capital Loan will be set forth in the NGP Credit Agreement.

In addition, under the NGP Agreement, NGP has agreed to provide a line of credit of up to $5.0 million to the Company following NDA approval of Gimoti, if any, and for a period of up to nine months thereafter. The line of credit will be extended pursuant to a credit agreement between the parties. NGP will receive a low single digit percentage on net sales of Gimoti in lieu of any interest on the line of credit (the “NGP Credit Fee”); provided that in no event shall the cumulative NGP Credit Fee exceed twice the amount of the principal borrowed by the Company. The line of credit will mature on the earlier of 30 days following the date the NGP Credit Fee is twice the amount of the borrowed principal and the two-year anniversary of the date the principal is borrowed by the Company. In the event the Company secures financing from a third-party wholesale distributor for the purchase of Gimoti for launch in excess of $2.5 million dollars, NGP will no longer be required to offer the line of credit.

The term of the NGP Agreement is five years from the date of commercial launch of Gimoti, if any, after which the Company will recapture 100% of product sales and assume all corresponding responsibilities. Within 30 days after each one-year anniversary of the NGP Agreement, either party may terminate the NGP Agreement if net sales of Gimoti do not meet certain annual thresholds. Either party may terminate the NGP Agreement for the material breach of the other party, subject to a 60-day cure period, or in the event an insolvency petition of the other party is pending for more than 60 days. Either party may also terminate the NGP Agreement upon
30-days written notice to the other party if Gimoti is subject to a safety recall, the parties are unable to agree to a commercialization plan and budget by a specified date, or if the Contribution Profit is negative for any calendar quarter beginning with the first full calendar quarter nine months following commercial launch. In addition, NGP may terminate the NGP Agreement if the Company withdraws Gimoti from the market for more than 180 days or if the Company is unable to provide product samples for use by the salesforce in a timely manner. NGP may also terminate the NGP Agreement, including the obligation to provide a line of credit, since Gimoti was not approved by FDA by April 30, 2019, but, as of August 7, 2019, has not elected to do so. The Company may terminate the NGP Agreement upon a change of control of the Company, subject to a one-time payment equal to between four times and one times annualized service fees paid by the Company under the NGP Agreement, with such amount based on which year (between one and five years) after commercial launch the change of control occurs, provided if the change of control occurs within one year of commercial launch, such amount will be the greater of the specified annualized service fee amount and $5 million.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Use of Estimates

Contract Research Organizations and Consultants

Warrant Accounting

Stock-Based Compensation

Research and Development Expenses

Net Loss Per Share

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Common stock subject to repurchase	—			30,165	—			37,582
Warrants to purchase common stock		2,713,561		2,797,561		2,713,561		2,797,561
Common stock options		3,232,871		3,017,624		3,232,871		3,017,624
Employee stock purchase plan	—			19,144	—			26,047
Total excluded securities		5,946,432		5,864,494		5,946,432		5,878,814

Recent Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2019

Accounting Policies [Abstract]

Summary of Outstanding Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share

For the periods presented, the following table sets forth the outstanding potentially dilutive securities that have been excluded from the calculation of diluted net loss per share because their inclusion would be anti-dilutive:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Common stock subject to repurchase	—			30,165	—			37,582
Warrants to purchase common stock		2,713,561		2,797,561		2,713,561		2,797,561
Common stock options		3,232,871		3,017,624		3,232,871		3,017,624
Employee stock purchase plan	—			19,144	—			26,047
Total excluded securities		5,946,432		5,864,494		5,946,432		5,878,814

Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2019

Equity [Abstract]

Summary of Estimated Fair Value of Stock Option Award

	Three Months Ended June 30,		Six Months Ended June 30,
	2019	2018	2019	2018
Common Stock Options
Risk free interest rate	1.80%-2.36%	2.85%	1.80%-2.55%	2.66%-2.85%
Expected option term	4.27-5.77 years	5.5 years	4.27-6.0 years	5.5-6.0 years
Expected volatility of common stock	101.46%-112.58%	92.30%	90.34%-112.58%	90.15%-92.30%
Expected dividend yield	0.0%	0.0%	0.0%	0.0%

Summary of Estimated Fair Value of Shares to be Acquired under Employee Stock Purchase Plan

	Six Months Ended June 30,
	2019	2018
Employee Stock Purchase Plan
Risk free interest rate	2.52%	1.85%
Expected term	0.5 years	0.5 years
Expected volatility of common stock	130.36%	58.76%
Expected dividend yield	0.0%	0.0%

Summary of Recognized Non-Cash Stock-Based Compensation Expense

The Company recognized non-cash stock-based compensation expense to employees and directors in its research and development and its general and administrative functions as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development	$	202,117	$	168,733	$	354,291	$	357,510
General and administrative		142,724		218,696		369,509		423,694
Total stock-based compensation expense	$	344,841	$	387,429	$	723,800	$	781,204

Organization and Basis of Presentation - Additional Information (Detail)		6 Months Ended
	May 15, 2019 d $ / shares	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Organization And Basis Of Presentation [Abstract]
Month and year of incorporation		2007-01
Cash and cash equivalents \| $		$ 7,440,079	$ 5,319,004	$ 6,531,079	$ 7,679,267
Minimum common stock closing bid price \| $ / shares	$ 1.00
Initial period to regain compliance	180 days
Number of minimum consecutive business days \| d	10
Closing bid price description		On May 15, 2019, the Company received a letter from Nasdaq indicating that, for the last thirty consecutive business days, the bid price for the Company’s common stock had closed below the minimum $1.00 per share requirement for continued listing on The Nasdaq Capital Market. In accordance with Nasdaq listing rules, the Company has been provided an initial period of 180 calendar days, or until November 11, 2019, to regain compliance. The letter states that Nasdaq will provide written notification that the Company has achieved compliance with its rules if at any time before November 11, 2019, the bid price of the Company’s common stock closes at $1.00 per share or more for a minimum of ten consecutive business days. The Nasdaq letter has no immediate effect on the listing or trading of the Company’s common stock and the common stock will continue to trade on The Nasdaq Capital Market.

Technology Acquisition Agreement - Additional Information (Detail)	1 Months Ended		6 Months Ended
	May 31, 2014 USD ($)	Jun. 30, 2007 USD ($)	Jun. 30, 2019 USD ($) Milestone
Technology Acquisition Agreement [Line Items]
Payment expensed as in-process research and development		$ 650,000
Mallinckrodt Plc [Member]
Technology Acquisition Agreement [Line Items]
Milestone payments contingent amount			$ 5,000,000
Number of milestone payments \| Milestone			1
Mallinckrodt Plc [Member] \| Rights and Patents Acquired from Questcor Pharmaceuticals Inc [Member] \| Maximum [Member]
Technology Acquisition Agreement [Line Items]
Milestone payments contingent amount			$ 52,000,000
Development Target One [Member] \| Rights and Patents Acquired from Questcor Pharmaceuticals Inc [Member]
Technology Acquisition Agreement [Line Items]
Milestone payment	$ 500,000
Development targets description			Upon the initiation of the first patient dosing in the Company's Phase 3 clinical trial for Gimoti.
Development Target Four [Member] \| Mallinckrodt Plc [Member] \| Patented Technology [Member]
Technology Acquisition Agreement [Line Items]
Development targets description			Depend on Gimoti's commercial success and will only apply if Gimoti receives regulatory approval. In addition, the Company will be required to pay to Mallinckrodt a low single digit royalty on net sales of Gimoti.
Milestone payments contingent amount			$ 47,000,000
Expected expiration of patent right			2032

Stockholders' Equity - Stock-Based Compensation - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stockholders' equity, stock split, conversion ratio	0.75
Stock options exchanged \| shares	2,456,999
Stock options issued \| shares	1,842,746
Exercise price \| $ / shares	$ 0.62
Share-based compensation expense \| $	$ 84,000
Share-based compensation arrangement, vesting period	4 years
Unrecognized compensation costs \| $	$ 2,700,000
Weighted average period	1 year 4 months 24 days

Stockholders' Equity - Summary of Estimated Fair Value of Stock Option Award (Detail) - Common stock options [Member]	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate		2.85%
Expected option term		5 years 6 months
Expected volatility of common stock		92.30%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Minimum [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate	1.80%		1.80%	2.66%
Expected option term	4 years 3 months 7 days		4 years 3 months 7 days	5 years 6 months
Expected volatility of common stock	101.46%		90.34%	90.15%
Maximum [Member]
Stock-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate	2.36%		2.55%	2.85%
Expected option term	5 years 9 months 7 days		6 years	6 years
Expected volatility of common stock	112.58%		112.58%	92.30%

Commercial Services Agreement - Additional Information (Detail)	Jan. 05, 2019 USD ($)
NGP Credit Agreement [Member]
Commercial Services Agreement [Line Items]
Line of credit	$ 5,000,000
Third-Party Wholesale Distributor [Member] \| NGP Credit Agreement [Member]
Commercial Services Agreement [Line Items]
Minimum financing arrangements from purchase order not to avail line of credit.	$ 2,500,000
NGP Agreement [Member]
Commercial Services Agreement [Line Items]
Term of agreement	5 years
Recapture percentage of product sales after agreement term	100.00%
Minimum termination fee	$ 5,000,000
Agreement termination fee description	The Company may terminate the NGP Agreement upon a change of control of the Company, subject to a one-time payment equal to between four times and one times annualized service fees paid by the Company under the NGP Agreement, with such amount based on which year (between one and five years) after commercial launch the change of control occurs, provided if the change of control occurs within one year of commercial launch, such amount will be the greater of the specified annualized service fee amount and $5 million.
NGP Agreement [Member] \| Gimoti [Member] \| Minimum [Member]
Commercial Services Agreement [Line Items]
Percentage of product profits	80.00%

Commitments - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
Commitments - Additional Information (Detail) - USD ($)	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019
Commitments And Contingencies Disclosure [Abstract]
Lease commencement date			Jan. 01, 2017
Lease expiry date			Dec. 31, 2019
Rent expense	$ 36,000	$ 35,000	$ 74,000	$ 69,000
Operating lease incremental borrowing rate			12.00%
Operating lease ROU	$ 69,795		$ 69,795		$ 136,000
Operating lease liability					$ 136,000

Stockholders' Equity - Common Stock - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Nov. 30, 2017
Sale Of Stock [Line Items]
Common stock, shares issued	24,113,956		17,427,533
Proceeds from issuance of common stock, net	$ 5,676,388	$ 3,431,520
FBR Sales Agreement [Member]
Sale Of Stock [Line Items]
Common stock, shares issued	6,686,423	1,485,054
Common stock , weighted average price per share	$ 0.87	$ 2.38
Proceeds from issuance of common stock, net	$ 5,700,000	$ 3,400,000
FBR Sales Agreement [Member] \| Maximum [Member]
Sale Of Stock [Line Items]
Common stock, value of shares issuable				$ 16,000,000

Stockholders' Equity - Warrants - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended	6 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Jun. 30, 2018
Sale Of Stock [Line Items]
Change in fair value of warrant liability			$ 433,392
Warrant Amendments [Member]
Sale Of Stock [Line Items]
Unregistered warrants to purchase of common stock		2,449,129
Change in fair value of warrant liability		$ 433,000
Reclassification of warrant liability to Additional Paid-in Capital		$ 3,300,000
Amendment date		2018-03
Underwriters [Member]
Sale Of Stock [Line Items]
Unregistered warrants to purchase of common stock expired	84,000

Condensed Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	24,113,956	17,427,533
Common stock, shares outstanding	24,113,956	17,427,533