Revenue Recognition We generate revenue principally from the sale of Probuphine in the U.S., collaborative research and development arrangements, technology licenses and sales, and government grants. Consideration received for revenue arrangements with multiple components is allocated among the separate performance obligations based upon their relative estimated standalone selling price. In determining the appropriate amount of revenue to be recognized as we fulfill our obligations under our agreements, we perform the following steps for our revenue recognition: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) we satisfy each performance obligation. Net Product Revenue We recognize revenue from product sales when control of the product transfers, generally upon shipment or delivery, to our customers, which include distributors. As customary in the pharmaceutical industry, our gross product revenue is subject to a variety of deductions in the forms of variable consideration, which include rebates, chargebacks, returns and discounts, in arriving at reported net product revenue. This variable consideration is estimated using the most-likely amount method, which is the single most-likely outcome under a contract and is typically at stated contractual rates. The actual outcome of this variable consideration may materially differ from our estimates. From time to time, we will adjust our estimates of this variable consideration when trends or significant events indicate that a change in estimate is appropriate to reflect the actual experience. Additionally, we will continue to assess the estimates of our variable consideration as we continue to accumulate additional historical data. Changes in the estimates of our variable consideration could materially affect our financial statements. Returns  Consistent with the provisions of ASC 606, we estimate returns at the inception of each transaction, based on multiple considerations, including historical sales, historical experience of actual customer returns, levels of inventory in our distribution channel, expiration dates of purchased products and significant market changes which may impact future expected returns to the extent that we would not reverse any receivables, revenues, or contract assets already recognized under the agreement. During the six months ended June 30, 2019, we entered into agreements with large national specialty pharmacies with a distribution channel different from that of our existing customers and, therefore, the related reserves have unique considerations. We will continue to evaluate the activities with these specialty pharmacies during upcoming quarters and will update the related reserves accordingly. Rebates  Our provision for rebates is estimated based on our customers contracted rebate programs and our historical experience of rebates paid. Discounts The provision is estimated based upon invoice billings, utilizing historical customer payment experience. The following table provides a summary of activity with respect to our product returns, and discounts and rebates, which are included on our condensed consolidated balance sheets within accrued sales allowances (in thousands): Product Discounts and Returns Rebates Allowance Allowance Total Balance at December 31, 2018 $ 33 $ 48 $ 81 Provision 766 156 922 Payments/credits (40) (133) (173) Balance at June 30, 2019 $ 759 $ 71 $ 830 Performance Obligations A performance obligation is a promise in a contract to transfer a distinct good or service to the customer. Our performance obligations include commercialization license rights, development services and services associated with the regulatory approval process. We have optional additional items in contracts, which are accounted for as separate contracts when the customer elects such options. Arrangements that include a promise for future commercial product supply and optional research and development services at the customers discretion are generally considered as options. We assess if these options provide a material right to the customer and, if so, such material rights are accounted for as separate performance obligations. If we are entitled to additional payments when the customer exercises these options, any additional payments are recorded in revenue when the customer obtains control of the goods or services. Transaction Price We have both fixed and variable consideration. Non-refundable upfront payments are considered fixed, while milestone payments are identified as variable consideration when determining the transaction price. Funding of research and development activities is considered variable until such costs are reimbursed at which point they are considered fixed. We allocate the total transaction price to each performance obligation based on the relative estimated standalone selling prices of the promised goods or services for each performance obligation. At the inception of each arrangement that includes milestone payments, we evaluate whether the milestones are considered probable of being achieved and estimate 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 value of the associated milestone is included in the transaction price. Milestone payments that are not within our control, such as approvals from regulators, are not considered probable of being achieved until those approvals are received. For arrangements that include sales-based royalties or earn-out payments, including milestone payments based on the level of sales, and the license or purchase agreement is deemed to be the predominant item to which the royalties or earn-out payments relate, we recognizes revenue at the later of (a) when the related sales occur, or (b) when the performance obligation to which some or all of the royalty or earn-out payment has been allocated has been satisfied (or partially satisfied). Allocation of Consideration As part of the accounting for these arrangements, we must develop assumptions that require judgment to determine the stand-alone selling price of each performance obligation identified in the contract. Estimated selling prices for license rights are calculated using the residual approach. For all other performance obligations, we use a cost-plus margin approach. Timing of Recognition Significant management judgment is required to determine the level of effort required under an arrangement and the period over which we expect to complete our performance obligations under an arrangement. We estimate the performance period or measure of progress at the inception of the arrangement and re-evaluate it each reporting period. This re-evaluation may shorten or lengthen the period over which revenue is recognized. Changes to these estimates are recorded on a cumulative catch up basis. If we cannot reasonably estimate when our performance obligations either are completed or become inconsequential, then revenue recognition is deferred until we can reasonably make such estimates. Revenue is then recognized over the remaining estimated period of performance using the cumulative catch-up method. Revenue is recognized for licenses or sales of functional intellectual property at the point in time the customer can use and benefit from the license. For performance obligations that are services, revenue is recognized over time proportionate to the costs that we have incurred to perform the services using the cost-to-cost input method.