The following is a summary of significant accounting policies followed in the preparation of these consolidated financial statements.

Basis of Presentation

The accompanying consolidated financial statements include those of the Company and its subsidiaries after elimination of all intercompany accounts and transactions. The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).

Use of Estimates

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

Cash and Cash Equivalents

The Company considers all highly liquid investments with an original maturity of 90 days or less at the date of purchase to be cash equivalents. As of December 31, 2019 and December 31, 2018, cash equivalents were comprised of cash equivalents, commercial paper and money market funds.

Marketable securities

Marketable securities consist of investments with original maturities greater than 90 days. The Company has classified its investments with maturities beyond one year as short-term, based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. The Company considers its investment portfolio of marketable securities to be available-for-sale. Accordingly, these investments are recorded at fair value, which is based on quoted market prices. Unrealized gains and losses are reported as the accumulated other comprehensive items in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other expense, net, based on the specific identification method. When determining whether a decline in value is other than temporary, the Company considers several factors, including whether the Company has the intent to sell the security, and whether it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis.  No declines in value were deemed to be other than temporary during the years ended December 31, 2019 and December 31, 2018.

Restricted Cash

For the initial facility of the Company, a deposit of $39,000 was restricted from withdrawal as of December 31, 2019 and 2018. The restriction is related to securing the initial lease and the restriction will expire in 2024, in accordance with the most recent amendment to the operating lease agreement. A deposit of $0.3 million was restricted from withdrawal as of December 31, 2019 and 2018.  The restriction is related to securing an amendment to the lease of the initial facility of the Company and the restriction will expire in 2024, in accordance with the most recent amendment to the operating lease agreement.  These balances are included in restricted cash on the accompanying consolidated balance sheets.  

A deposit of $0.5 million was restricted from withdrawal as of December 31, 2019 and 2018. The restriction is related to securing the separate facility lease on the second multi-tenant building in May 2016 and the restriction will expire in 2024, in accordance with the most recent amendment to the operating lease agreement. A deposit of $0.4 million was restricted from withdrawal as of December 31, 2018.  The restriction is related to securing an amendment to the lease of the separate facility of the Company and the restriction will expire in 2024, in accordance with the most recent amendment to the operating lease agreement. These balances are included in restricted cash on the accompanying consolidated balance sheets.

A deposit of $0.4 million was restricted from withdrawal as of December 31, 2019 and 2018.  The restriction is related to securing a separate facility lease on the third multi-tenant building in December 2018 that will expire on February 29, 2024, under which, beginning on March 1, 2019, the Company will rent 15,975 square feet of additional office space. The restriction will expire in 2024, in accordance with the operating lease agreement. This balance is included in restricted cash on the accompanying consolidated balance sheet.

A deposit of $0.7 million was restricted from withdrawal as of December 31, 2019 and 2018.  The restriction is related to securing leases on automobiles for employees who are based in the field. The restriction will expire in 2021, in accordance with the lease agreement. This balance is included in restricted cash on the accompanying consolidated balance sheet.

Accounts Receivable

The Company’s trade accounts receivable consist of amounts due from specialty distributors; specialty pharmacies; and medically-supervised healthcare settings that have been certified under a Risk Evaluation and Mitigation Strategy, or REMS, program, in the U.S. related to sales of ZULRESSO and have standard payment terms that generally require payment within 30 to 90 days from the invoice date. The Company monitors the financial performance and creditworthiness of customers so that it can properly assess and respond to changes in their credit profile. The Company reserves against trade accounts receivable for estimated losses that may arise from a customer’s inability to pay and any amounts determined to be uncollectible are written off against the reserve when it is probable that the receivable will not be collected. Trade accounts receivable are included in prepaid expenses and other current assets on the consolidated balance sheets and the amount was not significant as of December 31, 2019.

Inventory

Inventory is stated at the lower of cost or estimated net realizable value with cost determined on a first-in, first-out basis. Inventory costs include raw materials, third-party contract manufacturing, third-party packaging services, and freight. Raw and intermediate materials that may be utilized for either research and development or commercial purposes are identical and, as a result, are both classified as inventory. Amounts in inventory associated with research and development are charged to research and development expense when the product enters the research and development process and can no longer be used for commercial purposes and, therefore, does not have an “alternative future use” as defined in authoritative guidance. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period and writes down any excess and obsolete inventory to its estimated net realizable value in the period it is identified. If they occur, such impairment charges are recorded as a component of cost of goods sold in the consolidated statements of operations and comprehensive loss. Inventory is included in prepaid expenses and other current assets on the consolidated balance sheets and the amount was not significant as of December 31, 2019.

Prior to the initial date regulatory approval is received, costs related to the production of inventory are recorded as research and development expense on the Company’s consolidated statements of operations and comprehensive loss in the period incurred. The Company received FDA approval for ZULRESSO on March 19, 2019 and subsequently began capitalizing costs related to inventory manufacturing.

Property and Equipment

Property and equipment are recorded at cost and depreciated over their estimated useful lives using the straight-line method. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is credited or charged to income. Repairs and maintenance costs are expensed as incurred.

Intangible assets

The Company had no intangible assets as of December 31, 2018. The Company received FDA approval for ZULRESSO on March 19, 2019, and as a result, the Company was required to pay to CyDex Pharmaceuticals, Inc. (“CyDex”) and The Regents of the University of California milestone payments of $3.0 million and $0.5 million, respectively. At March 31, 2019, the amount of these milestones was capitalized as an intangible asset, and will be amortized to cost of goods sold over the expected useful life of the asset.

Leases

The Company determines if an arrangement is a lease at contract inception. Operating lease assets represent the Company’s right to use an underlying asset for the lease term and operating lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease assets and liabilities are recognized at the commencement date of the lease based upon the present value of lease payments over the lease term. When determining the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. The Company uses the implicit interest rate when readily determinable and uses the Company’s incremental borrowing rate when the implicit rate is not readily determinable based upon the information available at the commencement date in determining the present value of the lease payments.

The lease payments used to determine the Company’s operating lease assets may include lease incentives, stated rent increases and escalation clauses linked to rates of inflation, when determinable, and are recognized in the Company’s operating lease assets in the Company’s consolidated balance sheets. In addition, the Company’s contracts contain lease and non-lease components. The Company combines lease and non-lease components, which are accounted for together as lease components.

The Company’s operating leases are reflected in the right-of-use operating asset; operating lease liability, current portion; and operating lease liability, net of current portion in the Company’s consolidated balance sheets. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. Short-term leases, defined as leases that have a lease term of 12 months or less at the commencement date, are excluded from this treatment and are recognized on a straight-line basis over the term of the lease.

Variable lease payments are the amounts owed by the Company to a lessor that are not fixed, such as reimbursement for common area maintenance and utilities costs for facility leases; maintenance and tolls for leased vehicles, and are expensed when incurred.

Impairment of Long-Lived Assets

Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets.

Cost of Goods Sold

Cost of goods sold includes direct and indirect costs related to the manufacturing and distribution of ZULRESSO, including third-party manufacturing costs, packaging services, freight, third-party royalties payable on the Company’s net product revenues and amortization of intangible assets associated with ZULRESSO. Cost of goods sold may also include period costs related to certain inventory manufacturing services, inventory adjustment charges, as well as manufacturing variances. In connection with the FDA approval of ZULRESSO on March 19, 2019, the Company subsequently began capitalizing inventory manufactured or purchased after this date. As a result, certain manufacturing costs associated with product shipments of ZULRESSO were expensed prior to FDA approval and, therefore, are not included in cost of goods sold during the current period.

Research and Development Costs and Accruals

Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries and benefits, overhead costs, depreciation, contract services and other related costs. Research and development costs are expensed to operations as the related obligation is incurred.

The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the U.S. These agreements are generally cancelable, and related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research and development costs. When billing terms under these contracts do not coincide with the timing of when the work is performed, the Company is required to make estimates of outstanding obligations to those third parties as of the end of the reporting period.  Any accrual estimates are based on a number of factors, including the Company’s knowledge of the progress towards completion of the research and development activities, invoicing to date under the contracts, communication from the research institution or other companies of any actual costs incurred during the period that have not yet been invoiced, and the costs included in the contracts. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made by the Company. The historical accrual estimates made by the Company have not been materially different from the actual costs.

Patent Costs

The Company expenses patent costs as incurred and classifies such costs as selling, general and administrative expenses in the accompanying consolidated statements of operations and comprehensive loss.

Stock-Based Compensation

The Company recognizes compensation expense for stock-based awards, including grants of stock options and restricted stock units, made to employees and non-employee directors based on the estimated fair value on the date of grant, over the requisite service period. The Company recognizes stock-based compensation expense for only the portion of awards that are expected to vest.

Effective January 1, 2019, the Company recognizes compensation expense for stock-based awards, including grants of stock options and restricted stock units, made to non-employee consultants based on the estimated fair value on the date of grant, over the requisite service period. Through December 31, 2018, the Company recognized compensation expense for stock-based awards granted to non-employee consultants based on the fair value of the awards on each date on which the awards vest. Compensation expense was recognized over the vesting period, provided that services were rendered by such non-employee consultants during that time. At the end of each financial reporting period, the fair value of unvested options was re-measured using the then-current fair value of the common stock of the Company and updated assumptions using the Black-Scholes option-pricing model.

For awards that vest upon achievement of a performance condition, the Company recognizes compensation expense when achievement of the performance condition is met or during the period from which meeting the condition is deemed probable until the expected date of meeting the performance condition.

The fair value of each option grant is estimated using the Black-Scholes option-pricing model. Through December 31, 2015, the Company lacked sufficient Company-specific historical and implied volatility information, and as a result, the Company used the volatility of a group of publicly-traded peer companies in the Black-Scholes calculations.  Beginning in 2016, the Company estimated its expected volatility using a weighted average of the historical volatility of publicly-traded peer companies and the volatility of its common stock and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its common stock price for the duration of the expected term. The expected term of the options granted to employees and non-employee directors by the Company has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. Through December 31, 2018, the expected term of its options granted to non-employee consultants has been determined based on the contractual term of the options, and effective January 1, 2019, the “simplified” method is used. 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. The expected dividend yield is 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.

The Company also applies a forfeiture rate in order to calculate stock-based compensation expense. Expected forfeitures are based on the historical experience of the Company and management’s expectations of future forfeitures. To

the extent actual forfeitures differ from the estimates, the difference is recorded as a cumulative adjustment in the period in which the estimates are revised.

Treasury Stock

The Company records treasury stock at cost.  Treasury stock consists of shares received from an employee as consideration for exercises of stock options.

Basic and Diluted Net Loss Per Share

Basic net loss per share is computed by dividing the net loss by the weighted average number of common shares outstanding for the period. For periods in which the Company has reported net losses, diluted net loss per share is the same as basic net loss per share, because dilutive common shares are not assumed to have been issued if their effect is antidilutive.

The Company reported a net loss for the years ended December 31, 2019, 2018 and 2017.

Risks and Uncertainties

The product candidates developed by the Company require approvals from the U.S. Food and Drug Administration or foreign regulatory agencies prior to commercial sales. There can be no assurance that the current and future product candidates of the Company will receive the necessary approvals. If the Company fails to successfully complete clinical development and generate results sufficient to file for regulatory approval or is denied approval or approval is delayed, it may have a material adverse impact on the Company’s business and its financial statements.

Concentration of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company maintains accounts for all cash and cash equivalents at accredited financial institutions, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. The Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.

Income Taxes

The Company accounts for income taxes under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted rates in effect for the year in which these temporary differences are expected to be recovered or settled. Valuation allowances are provided if, based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. The Company accrues for potential interest and penalties related to unrecognized tax benefits in income tax expense.

Fair Value Measurements

Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Financial assets and liabilities carried at fair value are classified and disclosed in one of the following three categories:

The Company’s cash equivalents and marketable securities at December 31, 2019 and 2018 were carried at fair value, determined according to the fair value hierarchy; see Footnote 3, Fair Value Measurements.

The carrying amounts reflected in the consolidated balance sheets for accounts payable and accrued expenses approximate their fair values due to their short-term maturities at December 31, 2019 and 2018, respectively.

Segment Data

The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The singular focus of the Company is developing and commercializing novel medicines with the potential to transform the lives of people with debilitating disorders of the brain.

Comprehensive Loss

Comprehensive loss includes net loss and other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders.

Public Offerings

On July 23, 2014, the Company completed the sale of 5,750,000 shares of its common stock in its IPO at a price to the public of $18.00 per share, resulting in net proceeds to the Company of $94.0 million after deducting underwriting discounts and commissions and offering costs paid by the Company. The shares began trading on the Nasdaq Global Market on July 18, 2014.

On April 20, 2015, the Company completed the sale of 2,628,571 shares of its common stock at a price to the public of $52.50 per share, resulting in net proceeds to the Company of $129.1 million after deducting underwriting discounts and commissions and offering costs paid by the Company.

On January 12, 2016, the Company completed the sale of 3,157,894 shares of its common stock at a price to the public of $47.50 per share, resulting in net proceeds to the Company of $140.4 million after deducting underwriting discounts and commissions and offering costs paid by the Company.

On September 14, 2016, the Company completed the sale of 5,062,892 shares of its common stock at a price to the public of $39.75 per share, resulting in net proceeds to the Company of $189.2 million after deducting underwriting discounts and commissions paid by the Company.

On November 17, 2017, the Company completed the sale of 4,058,822 shares of its common stock at a price to the public of $85.00 per share, resulting in net proceeds to the Company of $325.8 million after deducting underwriting discounts and commissions and offering costs paid by the Company.

On February 13, 2018, the Company completed the sale of 4,032,012 shares of its common stock at a price to the public of $164.00 per share, resulting in net proceeds to the Company of $631.2 million after deducting underwriting discounts and commissions and offering costs paid by the Company.

On February 27, 2019, the Company completed the sale of 3,833,334 shares of its common stock at a price to the public of $150.00 per share, resulting in net proceeds to the Company of $560.9 million after deducting underwriting discounts and commissions and offering costs paid by the Company.

Revenue Recognition

Effective January 1, 2017, the Company adopted Accounting Standards Codification (“ASC”), Topic 606, Revenue from Contracts with Customers (“Topic 606”). This standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as collaboration arrangements and leases. The adoption of Topic 606 had no impact on the Company’s consolidated financial statements as the Company did not have any revenue prior to adoption.

The Company received approval of ZULRESSO from the FDA in March 2019 and subsequently began to record revenues from product sales in June 2019. Prior to the second quarter of 2019, all of the revenues of the Company were derived from the Company’s collaboration agreement with Shionogi & Co., Ltd., (“Shionogi”). The terms of the Company’s collaboration agreement include consideration such as non-refundable license fees, reimbursement of any development costs the Company incurs on behalf of Shionogi, payments due upon the achievement of clinical and pre-clinical performance-based development milestones, regulatory milestones, manufacturing services to supply drug product for clinical trials, and sales-based milestones and royalties on product sales.

Under Topic 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price, including variable consideration, if any; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, they are considered performance obligations. The exercise of a material right may be accounted for as a contract modification or as a continuation of the contract for accounting purposes. For contracts determined to be within the scope of Topic 606, the Company assesses whether the goods or services promised within each contract are distinct to identify those that are performance obligations. This assessment involves subjective determinations and requires management to make judgments about the individual promised goods or services and whether such are separable from the other aspects of the contractual relationship. Promised goods and services are considered distinct provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. The Company allocates the transaction price (the amount of consideration it expects to be entitled to from a customer in exchange for the promised goods or services) to each performance obligation and recognizes the associated revenue when (or as) each performance obligation is satisfied. The Company’s estimate of the transaction price for each contract includes all variable consideration to which the Company expects to be entitled.

Collaboration and license revenue

In assessing whether a promised good or service is distinct in the evaluation of a collaboration or license arrangement subject to Topic 606, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. The Company also considers the intended benefit of the contract in assessing whether a promised good or service is separately identifiable from other promises in the contract. If a promised good or service is not distinct, the Company is required to combine that good or service with other promised goods or services until it identifies a bundle of goods or services that is distinct.

The transaction price is then determined and allocated to the identified performance obligations in proportion to their standalone selling prices (“SSP”) on a relative SSP basis. SSP is determined at contract inception and is not updated to reflect changes between contract inception and when the performance obligations are satisfied. Determining the SSP for performance obligations requires significant judgment. In developing the SSP for a performance obligation, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs.  In certain circumstances, the Company may apply the residual method to determine the SSP of a good or service if the standalone selling price is considered highly variable or uncertain. The Company validates the SSP for performance obligations by evaluating whether changes in the key assumptions used to determine the SSP will have a significant effect on the allocation of arrangement consideration between multiple performance obligations.

If the consideration promised in a contract includes a variable amount, the Company estimates the amount of consideration to which it will be entitled in exchange for transferring the promised goods or services to a customer. The Company determines the amount of variable consideration by using the expected value method or the most likely amount method. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment.

If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received.

In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company assessed its arrangement with Shionogi and concluded that a significant financing component does not exist. For arrangements with licenses of intellectual property that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes royalty revenue and sales-based milestones at the later of (i) when the related sales occur, or (ii) when the performance obligation to which the royalty has been allocated has been satisfied.

The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied at a point in time or over time, and if over time this is based on the use of an output or input method. To date, revenue from the Company’s collaboration agreement with Shionogi has come from an initial, upfront fee upon execution of the agreement and for the supply of drug product for Shionogi’s clinical trials.

Product revenue

The Company recognizes product revenues, net of variable consideration related to certain allowances and accruals that are determined using the expected value method, in its consolidated financial statements at the point in time when control transfers to the customer, which is typically when the product has been delivered to the customer’s location. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. The Company’s only performance obligation identified for ZULRESSO is to deliver the product to the location specified by the customer’s order. The Company records shipping and handling costs associated with delivery of product to its customers within selling, general and administrative expenses on its consolidated statements of operations and comprehensive loss. The Company expenses incremental costs of obtaining a contract as incurred if the expected amortization period of the asset would be less than one year. If the Company were to incur incremental costs with an amortization period greater than a year, such costs would be capitalized as contract assets, as they are expected to be recovered, and would be expensed by amortizing on a systematic basis that is consistent with the transfer to the customer of the goods or services to which the asset relates. The Company did not have any contract assets (unbilled receivables) at December 31, 2019, as customer invoicing generally occurs before or at the time of revenue recognition. The Company did not have any contract liabilities at December 31, 2019, as the Company did not receive any payments in advance of satisfying its performance obligations to its customers. Amounts billed or invoiced are included in prepaid expenses and other current assets on the consolidated balance sheets.

The Company records reserves, based on contractual terms, for the following components of variable consideration related to product sold during the reporting period, as well as its estimate of product that remains in the distribution channel inventory of its customers at the end of the reporting period. On a quarterly basis, the Company will update its estimates and record any necessary material adjustments in the period they are identified.

Chargebacks: The Company estimates chargebacks from its customers who directly purchase the product from the Company for discounts resulting from contractual commitments to sell products to eligible healthcare settings at prices lower than the list prices charged to its customers. Customers charge the Company for the difference between what they pay to the Company for the product and the selling price to the eligible healthcare settings. Reserves for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel inventories at the end of each reporting period that the Company expects will be sold to eligible healthcare settings, and chargebacks that customers have claimed, but for which the Company has not yet issued a credit.

Government Rebates: The Company is subject to discount obligations under government programs, including Medicaid. The Company records reserves for rebates in the same period the related product revenue is recognized, resulting in a reduction of ZULRESSO product revenues and a current liability that is included in accrued expenses on its consolidated balance sheets.  The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimates of future claims that will be made for product that has been recognized as revenue, but which remains in the distribution channel at the end of each reporting period.

Trade Discounts and Allowances: The Company generally provides customary invoice discounts on ZULRESSO sales to its customers for prompt payment and the Company pays fees for sales order management, data, and distribution services. The Company estimates its customers will earn these discounts and fees and deducts these discounts and fees in full from gross ZULRESSO revenues and accounts receivable at the time the Company recognizes the related revenues.

Financial Assistance: The Company provides voluntary financial assistance programs to patients with commercial insurance that have coverage and reside in states that allow financial assistance. The Company estimates the financial assistance amounts for ZULRESSO and records any such amounts within accrued expenses on its consolidated balance sheets. The calculation of the accrual for financial assistance is based on an estimate of claims and the cost per claim that the Company expects to receive using demographics for patients who have registered and been approved for assistance. Any adjustments are recorded in the same period the

related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability, which is included as a component of accrued expenses on the consolidated balance sheets.

Product Returns: Consistent with industry practice, the Company offers its customers that purchase ZULRESSO directly from the Company limited product return rights for damaged, defective or expiring product, provided it is within a specified period around the product expiration date as set forth in the applicable individual distribution agreement. The Company estimates the amount of its product sales that may be returned by its customers and records this estimate as a reduction of revenue in the period the related product revenue is recognized, as well as a reserve within accrued expenses on the consolidated balance sheets. Based on the distribution model for ZULRESSO, contractual inventory limits with its customers, the product price and limited contractual return rights, the Company believes there will be minimal ZULRESSO returns. The Company has experienced no product returns to date. The Company will update its estimated refund liability, on at least a quarterly basis, based on actual shipments of ZULRESSO subject to contractual return rights, changes in expectations about the amount of estimated refunds or actual returns.

Recently Issued Accounting Pronouncements

In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-02, Leases, which replaced the existing guidance in ASC 840, “Leases”. The FASB subsequently issued the following amendments to ASU No. 2016-02 that have the same effective date and transition date: ASU No. 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842; ASU No. 2018-10, Codification Improvements to Topic 842, Leases; ASU No. 2018-11, Leases (Topic 842): Targeted Improvements; ASU No. 2018-20, Narrow-Scope Improvement for Lessors; and ASU No. 2019-01, Leases (Topic 842): Codification Improvements. The Company adopted these amendments with ASU No. 2016-02 effective January 1, 2019. The ASC 842 standard generally requires lessees to recognize operating and financing lease liabilities and corresponding right-of-use assets on the consolidated balance sheets and to provide enhanced disclosures surrounding the amount, timing and uncertainty of cash flows arising from leasing arrangements. The Company adopted ASC 842 using the modified retrospective approach with an effective date of January 1, 2019 for leases that existed on that date. Prior period results continue to be presented under ASC 840 based on the accounting standards originally in effect for such periods. Presentation of leases within the consolidated statements of operations and comprehensive loss and consolidated statements of cash flows is generally consistent with the former lease accounting guidance. The Company elected the package of practical expedients permitted under the transition guidance and as such, the adoption of this ASU did not change the classification of any of the Company’s leases. The Company elected to combine lease and non-lease components, elected not to record leases with an initial term of 12 months or less on the consolidated balance sheets and will recognize the associated lease payments in the consolidated statements of operations and comprehensive loss on a straight-line basis over the lease term.  On the implementation date, $44.2 million was recognized as total lease liabilities and $41.1 million was recognized as total right-of-use assets on the Company’s consolidated balance sheet.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, and subsequently issued amendments, which introduces a new methodology for accounting for credit losses on financial instruments, including available-for-sale debt securities. The guidance establishes a new "expected loss model" that requires entities to estimate current expected credit losses on financial instruments by using all practical and relevant information. Any expected credit losses are to be reflected as allowances rather than reductions in the amortized cost of available-for-sale debt securities. Early adoption is permitted for annual periods beginning after December 15, 2018, and interim periods therein. The Company adopted the standard on the required effective date of January 1, 2019. This guidance did not have a significant impact on the Company’s consolidated financial statements and related disclosures.

In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash that changes the presentation of restricted cash and cash equivalents in the statements of cash flows. Restricted cash and restricted cash equivalents will be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statements of cash flows. The Company adopted this standard during the first quarter of 2018. Restricted cash is now included as a component of cash, cash equivalents, and restricted cash on the Company’s consolidated statements of cash flows. Restricted cash balances are classified as non-current unless, under the terms of the applicable agreements, the funds will be released from restrictions within one year from the balance sheet date. The inclusion of restricted cash increased the beginning balances of the consolidated statements of cash flows by $2.4 million, $0.8 million and $0.6 million, respectively, and the ending balances by $2.4 million, $2.4 million and $0.8 million, respectively, for the years ended December 31, 2019, 2018 and 2017.

In June 2018, the FASB issued ASU No. 2018-07, Compensation—Stock Compensation (Topic 718) – Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”), which aligns the accounting for share-based payment awards issued to employees and non-employees. Under the new guidance, the existing guidance regarding employees will apply to share-based transactions with non-employees, as long as the transaction is not effectively a form of financing, with the exception of specific guidance related to the attribution of compensation cost. The cost of non-employee awards will continue to be recorded as if the grantor had paid cash for the goods or services. In addition, the contractual term will be able to be used in lieu of an expected term in the option-pricing model for non-employee awards. The Company adopted the standard on the required effective date of January 1, 2019. This guidance did not have a significant impact on the Company’s consolidated financial statements and related disclosures.

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. This standard modifies certain disclosure requirements on fair value measurements. The Company adopted the standard on the required effective date of January 1, 2020. This guidance is not expected to have a significant impact on the Company’s consolidated financial statements and related disclosures.

Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s consolidated financial statements upon adoption.

Restricted Stock Units

During the year ended December 31, 2017, the Company granted 32,500 restricted stock units to employees of the Company. The Company did not grant restricted stock units prior to January 1, 2017.  These restricted stock units vested ratably over two years, with cliff vesting of 50% at both the one-year and two-year anniversary of the grant date, which was in February 2018 and 2019, respectively. The fair value of restricted stock units that vested during the years ended December 31, 2019 and 2018 was $2.0 million and $2.6 million, respectively. No restricted stock units vested during the year ended December 31, 2017.    

During the year ended December 31, 2018, the Company granted 71,400 performance restricted stock units to employees of the Company. The milestones for 33,600 grants were not met, and accordingly, these grants were cancelled. 37,800 performance restricted stock units will vest upon the achievement of a certain commercial milestone. 

During the year ended December 31, 2019, the Company granted 393,539 performance restricted stock units to employees of the Company. These performance restricted stock units are related to the achievement of certain clinical and regulatory development milestones related to product candidates and commercial milestones.

Recognition of stock-based compensation expense associated with performance restricted stock units commences when the performance condition is considered probable of achievement, using management’s best estimates, which consider the inherent risk and uncertainty regarding the future outcomes of the milestones.

During the year ended December 31, 2019, one milestone was achieved for a grant that was made during the year. This milestone represents 18% of the performance restricted stock units that were granted during the year ended December 31, 2019.

The fair value of performance restricted stock units that vested during the year ended December 31, 2019 was $11.1 million. No performance restricted stock units vested during the year ended December 31, 2018.

The table below summarizes activity relating to restricted stock units:

At December 31, 2019, 333,243 performance restricted stock units were both outstanding and unvested, and the total unrecognized stock-based compensation expense related to those awards was $52.6 million.

Equity Plans

On July 2, 2014, the stockholders of the Company approved the 2014 Stock Option and Incentive Plan (the “2014 Plan”), which became effective immediately prior to the completion of the Company’s IPO. The 2014 Plan provides for the grant of restricted stock awards, restricted stock units, incentive stock options and non-statutory stock options. The 2014 Plan replaced the Company’s 2011 Stock Option and Grant Plan (the “2011 Plan”). The Company no longer grants stock options or other awards under its 2011 Plan, but any options outstanding under the 2011 Plan remain outstanding and effective.

The 2014 Plan provides for an annual increase, to be added on the first day of each fiscal year, by up to 4% of the Company’s outstanding shares of common stock as of the last day of the prior year.  On January 1, 2019, 1,875,530 shares of common stock, representing 4% of the Company’s outstanding shares of common stock as of December 31, 2018, were added to the 2014 Plan.

On December 15, 2016, the Board of Directors of the Company (the “Board”) approved the 2016 Inducement Equity Plan (the “2016 Plan”). The 2016 Plan provides for the grant of equity awards to individuals who have not previously been an employee or a non-employee director of the Company to induce them to accept employment and to provide them with a proprietary interest in the Company. On September 20, 2018, the Board amended the 2016 Plan to increase the total number of shares reserved for issuance under such plan by 1,200,000 shares.

Terms of equity grants, including vesting requirements, are determined by the Board or the Compensation Committee of the Board, subject to the provisions of the applicable plan. Options granted by the Company, that are not performance-based, generally vest based on the continued service of the grantee with the Company during a specified period following grant. These awards, when granted to employees, generally vest ratably over four years, with 25% cliff vesting at the one-year anniversary. All option awards expire in 10 years.

Performance-Based Stock Options

During the years ended December 31, 2018 and 2017, the Company granted 524,003 and 449,208 options, respectively, to employees to purchase shares of common stock that contain performance-based vesting criteria, primarily related to the achievement of certain clinical and regulatory development milestones related to product candidates and commercial milestones. During the year ended December 31, 2019, the Company did not grant performance-based stock options. Recognition of stock-based compensation expense associated with performance-based stock options commences when the performance condition is considered probable of achievement, using management’s best estimates, which consider the inherent risk and uncertainty regarding the future outcomes of the milestones.

During the year ended December 31, 2017, no milestones were achieved.

During the year ended December 31, 2018, a milestone was achieved under a stock option granted to a consultant. The milestone was related to the consummation of a licensing or corporate partnering arrangement.  During the year ended December 31, 2018, the Company recognized stock-based compensation expense related to this milestone of $6.9 million.

During the year ended December 31, 2018, one milestone was achieved.  This milestone represents 33% of the performance-based option grants that were made during the year ended December 31, 2017. During the year ended December 31, 2018, the Company recognized stock-based compensation expense related to this milestone of $4.4 million.  

During the year ended December 31, 2018, the remaining milestone for the performance-based option grants that were made during the years ended December 31, 2016 and December 31, 2015 was not met, and accordingly, those options were cancelled.  This milestone represents 50% and 35% of the performance-based option grants that were made during the years ended December 31, 2016 and December 31, 2015, respectively.  The Company recognized no stock-based compensation expense related to this milestone.

During the year ended December 31, 2019, one milestone was achieved. This milestone represents 20% and 33% of the performance-based option grants that were made during the years ended December 31, 2018 and 2017, respectively. During the year ended December 31, 2019, the Company recognized stock-based compensation expense related to this milestone of $16.3 million.

As of December 31, 2019, 2018 and 2017 for option grants that were outstanding, the achievement of the milestones that had not been met that are the criteria for vesting of performance-based stock options was considered not probable, and therefore no expense has been recognized related to these awards in the years ended December 31, 2019, 2018 and 2017, respectively.

Stock-Based Compensation Expense

Stock-based compensation expense recognized during the years ended December 31, 2019, 2018 and 2017 was as follows:

Stock-based compensation expense by award type recognized during the years ended December 31, 2019, 2018 and 2017 was as follows:

For stock option awards, the fair value is estimated at the grant date using the Black-Scholes option-pricing model, taking into account the terms and conditions upon which options are granted. The fair value of the options is amortized on a straight-line basis for awards to employees over the requisite service period of the awards. For awards to non-employees, the fair value of the options was amortized on a graded basis through December 31, 2018, and starting on January 1, 2019, on a straight-line basis, over the requisite service period of the awards. The weighted average grant date fair value per share of stock options granted under the Company’s equity plans during the years ended December 31, 2019, 2018 and 2017 was $82.39, $109.92 and $41.94, respectively.

The fair value of each option granted under the Company’s equity plans has been calculated on the date of grant using the following weighted average assumptions:

Expected dividend yield: the Company has not paid, and does not anticipate paying, any dividends in the foreseeable future.

Risk-free interest rate: the Company determined the risk-free interest rate by using a weighted average equivalent to the expected term based on the U.S. Treasury yield curve in effect as of the date of grant.

Expected volatility: the Company does not have sufficient history to support a calculation of volatility using only its historical data. Starting in 2016, the Company uses a weighted-average volatility considering the Company’s own volatility since the IPO in July 2014 and the volatilities of a peer group of comparable companies for time periods prior to the IPO.  Prior to 2016, the Company used volatilities based on an analysis of reported data for a peer group of comparable companies.

Expected term (in years): the expected term represents the period that the Company’s stock option grants are expected to be outstanding. The Company has been publicly-traded since July 2014, and there is not sufficient historical term data to calculate the expected term of the options. Therefore, the Company elected to utilize the “simplified” method to estimate the expected term of options granted to employees. Under this approach, the weighted average expected life is presumed to be the average of the vesting term and the contractual term of the option.

Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from estimates. The Company estimates forfeitures based on historical terminations. For the years ended December 31, 2019, 2018 and 2017, the weighted-average forfeiture rates were 13.7%, 10.7% and 13.3%, respectively.

Through December 31, 2018, for options granted to non-employees, the expected term is 10 years, which is the contractual term of each option. All other assumptions used to calculate the grant date fair value for non-employees are generally consistent with the assumptions used for options granted to employees.

Option Rollforward and Other

The table below summarizes activity related to time-based and performance-based stock options:

At December 31, 2019, the Company had unrecognized stock-based compensation expense related to its unvested service-based stock option awards of $283.4 million, which is expected to be recognized over the remaining weighted average vesting period of 2.44 years.

At December 31, 2019, 485,595 performance-based stock options were both outstanding and unvested, and the total unrecognized stock-based compensation expense related to those awards was $35.7 million.

The intrinsic value of stock options exercised during the years ended December 31, 2019, 2018 and 2017 was $119.1 million, $98.3 million and $77.7 million, respectively.

2014 Employee Stock Purchase Plan

On July 2, 2014, the Company’s stockholders approved the 2014 Employee Stock Purchase Plan, which had been previously approved by the Board of Directors. The 2014 Employee Stock Purchase Plan became effective upon the completion of the IPO. A total of 282,000 shares of common stock were authorized for issuance under this plan. As of December 31, 2019, 105,160 shares have been issued under this plan and 176,840 shares are available for issuance under this plan. At December 31, 2019, accrued expenses includes $0.7 million of stock-based compensation expense related to an enrollment period for which the related shares had not been issued as of December 31, 2019.

Shares Reserved and Available for Future Issuance

As of December 31, 2019, the total number of shares reserved under all equity plans was 10,651,531 and the total number of shares available for future issuance under all equity plans was 2,155,175.  

The table below summarizes activity relating to restricted stock units:

Stock-based compensation expense by award type recognized during the years ended December 31, 2019, 2018 and 2017 was as follows:

The table below summarizes activity related to time-based and performance-based stock options: