In December 2013, the Company adopted the 2013 Equity Incentive Plan (as subsequently amended and restated, the “Plan”), which provides for the issuance of options, stock appreciation rights, stock awards and stock units. Pursuant to Nasdaq listing rules, the Company issued inducement awards in December 2017 to the Company’s President outside of the Plan in the form of an option to purchase 775,000 shares of the Company’s common stock and a RSU award to purchase 40,000 shares of the Company’s common stock. In June 2018, the Company increased the aggregate number of shares of common stock authorized for issuance under the Plan by 2,500,000 shares. Stock option activity for employees and non-employees for the three months ended March 31, 2020 is as follows:

	Shares Issuable Pursuant to Stock Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Terms (years)		Total Intrinsic Value (in thousands)
Outstanding January 1, 2020		9,040,328		$	6.98		7.3	$	7,420

Granted		—		$	—
Exercised		(135,013	)	$	5.91
Forfeited		(105,356	)	$	9.63
Outstanding March 31, 2020		8,799,959		$	6.96		7.1	$	1,625
Exercisable March 31, 2020		5,614,559		$	6.69		6.4	$	1,586
Available for future grant		245,354

The weighted average grant-date fair value of stock options outstanding on March 31, 2020 was $5.01 per share. Total unrecognized compensation costs related to non-vested stock options at March 31, 2020 were approximately $15.8 million and are expected to be recognized within future operating results over a weighted-average period of 2.29 years. The total intrinsic value of the options exercised during the three months ended March 31, 2020, and 2019 was approximately $0.3 million and $0.2 million, respectively.

The expected term of the employee-related options was estimated using the “simplified” method as defined by the SEC’s Staff Accounting Bulletin No. 107, Share-Based Payment. The volatility assumption was determined by examining the historical volatilities for industry peer companies, as the Company did not have sufficient trading history for its common stock. The risk-free interest rate assumption is based on the U.S. Treasury instruments, the term of which was consistent with the expected term of the options. The dividend assumption is based on the Company’s history and expectation of dividend payouts. The Company has never paid dividends on its common stock and does not anticipate paying dividends on its common stock in the foreseeable future. Accordingly, the Company has assumed no dividend yield for purposes of estimating the fair value of the options.

The Company uses the Black-Scholes model to estimate the fair value of stock options granted. There were no stock options granted during the three months ended March 31, 2020, and 2019.

RSU activity under the Plan for the three months ended March 31, 2020 is as follows:

			Weighted- Average
			Grant Date
	RSUs		Fair Value
Unvested January 1, 2020		68,650	$	11.29
Granted		—	$	—
Vested		—	$	—
Forfeited		—	$	—
Unvested March 31, 2020		68,650	$	11.29

RSUs awarded to employees generally vest one-fourth per year over four years from the anniversary of the date of grant, provided the employee remains continuously employed with the Company. Shares of the Company’s stock are delivered to the employee upon vesting, subject to payment of applicable withholding taxes. The fair value of RSUs is equal to the closing price of the Company’s common stock on the date of grant. Total unrecognized compensation costs related to non-vested RSUs at March 31, 2020 was approximately $0.6 million and is expected to be recognized within future operating results over a period of 0.9 years. The following table presents stock-based compensation expense included in the Company’s consolidated statements of operations:

	Three Months Ended March 31,
	2020		2019
Research and development	$	681,613	$	700,263
General and administrative		1,516,574		1,761,436
Total	$	2,198,187	$	2,461,699