Significant Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]
Segment Reporting, Policy [Policy Text Block]	Segment Reporting We operate in one business segment focusing on the research, discovery, development and commercialization of small-molecule and protein therapeutics targeting immunologic diseases, including complement-mediated diseases and cancers related to dysfunction of the immune system, as well as addictive and compulsive disorders. The Company defines its operating segment based on internally reported financial information that is regularly used by the Chief Operating Decision Maker (“CODM”) to analyze performance, make decisions and allocate resources. The Company’s CODM is our Chief Executive Officer. For the three months ended March 31, 2026, the Company has identified one operating and reporting segment. The CODM reviews net income (loss) and expenses reported on the condensed consolidated statement of operations and comprehensive income (loss). The measurement of segment assets is reported on the condensed consolidated balance sheet as total consolidated assets. All long-lived assets are held in the U.S. Our segment net income (loss) aligns with our condensed consolidated statement of operations and comprehensive income (loss).
Revenue [Policy Text Block]	Revenue Recognition When we enter into a customer contract, we perform the following five steps: (i) identify the contract with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) we satisfy a performance obligation. Product Sales, Net We generally recognize revenue from product sales when the product is delivered to our wholesalers and title to the product is transferred, upon which we have satisfied our performance obligations. Fulfillment activities by the wholesalers are not considered to be a separate performance obligation. Product revenue is recorded net of variable consideration, including wholesaler distribution fees, chargebacks, returns and discounts. We estimate variable consideration using the expected value approach. This estimate is based on several factors, including: historical return rates, expiration date by product and estimated levels of inventory in the wholesale channel. Since there is often a timing lag between the product sale and the settlement of accruals relating to these programs, our net product revenue may incorporate revisions of accruals for several periods. We include such estimates in the transaction price only to the extent that it is probable that a significant reversal of revenue will not occur when the uncertainty associated with the variable consideration is subsequently resolved. Given the limited commercialization history of YARTEMLEA, our estimates of variable consideration require judgment and are subject to change as additional data becomes available. We recognize adjustments to net product revenue in the period in which changes in estimates become known. Chargebacks Chargebacks represent discounts provided to eligible covered entities under government programs, including the 340B Drug Pricing Program (“340B”) and the Medicaid Drug Rebate Program (“Medicaid”). In addition, we are subject to pricing obligations under our Federal Supply Schedule agreement with the U.S. government (the “FSS Agreement”), which establishes maximum prices for sales to certain federal agencies and may give rise to additional discounts and rebates. Chargebacks are recorded as a reduction of gross product revenue at the time of sale. Reserves for chargebacks are generally recorded as reductions of accounts receivable, while reserves for Medicaid rebates and patient co-pay assistance, if applicable, are recorded as accrued liabilities. Chargeback estimates are based on statutory pricing requirements applicable to the 340B program and expected utilization by covered entities. Given the limited commercial history of our recently launched product, these estimates require significant judgment, including assumptions related to future utilization patterns and channel inventory. Estimates are reassessed at each reporting period and adjusted as necessary based on actual experience, changes in 340B utilization, and other relevant factors. In addition to 340B chargebacks and Medicaid rebates, we maintain programs that may result in additional variable consideration, including a patient co-pay assistance program. There was no activity under the Medicaid and co-pay assistance program during the three months ended March 31, 2026, and, accordingly, no material related reductions to gross product revenue were recorded. We will continue to evaluate these programs as utilization evolves and will recognize the related reductions to revenue in the period in which they occur. Distribution Fees and Return Allowances We pay distribution fees to wholesalers for services they perform on our behalf. These fees are calculated based on the wholesalers’ average acquisition cost of purchases of YARTEMLEA, exclusive of any chargebacks. We estimate these amounts at the time of sale to the wholesaler and record them as a reduction in product sales in the same period the related revenue is recognized. We allow for the return of product up to 12 months past its expiration date or for product that is damaged. In estimating product returns, we take into consideration our return experience to date, the remaining shelf-life of product we have previously sold, inventory in the wholesale channel, and our expectation that product is typically not held by health care providers based on the frequency of their reorders. There were no product returns in the three months ended March 31, 2026. Due to the ordering patterns associated with transplant centers and the extended shelf life of YARTEMLEA, returns are expected to be limited; however, our estimates may change as commercial experience matures.
Cost of Goods and Service [Policy Text Block]	Cost of Product Sales Cost of product sales includes third-party manufacturing, royalties based on net product sales, and other costs directly related to the production and distribution of YARTEMLEA. We expensed as research and development expense all costs associated with the manufacture of YARTEMLEA produced prior to FDA approval. As a result, the cost basis of inventory available for sale at the time of commercialization was minimal, and cost of product sales is correspondingly low during the initial period following launch. Following FDA approval, we capitalize direct manufacturing costs as inventory and recognize these amounts in cost of product sales when the related inventory is sold. Accordingly, cost of product sales and gross margin during the initial periods following commercialization may not be indicative of future periods as we begin capitalizing and expensing post‑approval manufacturing costs.
Research and Development Expense, Policy [Policy Text Block]	Research and Development Research and development expenses are comprised primarily of contracted research and development activities, clinical trial study and manufacturing costs prior to approval; consulting services; contract milestones; materials and supplies; costs for personnel, including salaries, benefits, and stock-based compensation; depreciation; an allocation of our occupancy costs; and other expenses incurred to sustain our overall research and development programs. Advance payments for goods or services that will be used for future research and development activities are deferred and then recognized as an expense as the related goods are delivered or the services are performed. All other research and development costs are expensed as incurred.
Selling, General and Administrative Expenses, Policy [Policy Text Block]	Selling, General and Administrative Selling, general and administrative expenses are comprised primarily of marketing expenses; professional and legal services; patent costs; and salaries, benefits, and stock-based compensation costs for marketing and other personnel not directly engaged in research and development. Additionally, selling, general and administrative expenses include depreciation, an allocation of our occupancy costs, and other general corporate expenses. Advertising costs are expensed as incurred.
Share-Based Payment Arrangement [Policy Text Block]	Stock-Based Compensation Stock-based compensation expense is recognized for all share-based payments, including grants of stock option awards and restricted stock units based on estimated fair values. The fair value of our stock is calculated using the Black-Scholes option-pricing model, which requires assumptions around volatility, forfeiture rates, risk-free interest rate and expected term. Compensation expense is recognized over the requisite service periods, which is generally the vesting period, using the straight-line method. Forfeiture expense is estimated at the time of grant and revised in subsequent periods if actual forfeitures differ from those estimates.
Income Tax, Policy [Policy Text Block]	Income Taxes Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their tax basis. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be recovered or settled. We recognize the effect of income tax positions only if those positions are more likely than not to be sustained upon an examination by the relevant taxing authority. A valuation allowance is established when it is more likely than not that the deferred tax assets will not be realized.
Discontinued Operations, Policy [Policy Text Block]	Asset Sale Transactions The Company evaluates transactions involving the sale of our compounds, products or drug programs to determine whether such arrangements represent a sale of a business or a sale of a nonfinancial asset. Transactions that do not meet the definition of a business are accounted for as the sale of a nonfinancial asset under Accounting Standards Codification (“ASC”) 610‑20, Other Income—Gains and Losses from the Derecognition of Nonfinancial Assets. Upon transfer of control of the compound, product or drug program asset to a counterparty, the Company recognizes consideration received. Any excess of consideration over the carrying value of the asset sold is recognized as a gain in the condensed consolidated statements of operations. Potential Milestone Income The APLA with Novo Nordisk includes variable consideration in the form of milestone payments that are contingent upon the achievement of specified development, regulatory or commercialization events. The Company applies the variable consideration and constraint guidance in ASC 606, Revenue from Contracts with Customers, by analogy. At contract inception and throughout the term of the arrangement, the Company assesses whether the achievement of each milestone is probable and estimates variable consideration using the most likely amount method. Contingent milestone payments are excluded from the transaction price until the related milestone is achieved and it is probable that a significant reversal of cumulative revenue recognized will not occur. Amounts are included in the transaction price only to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. The Company re-evaluates the transaction price at each reporting period, including the estimated variable consideration and the application of the constraint, to reflect changes in circumstances. Factors considered in these evaluations include the clinical or technical complexity of the milestone, the stage of development, and the risk of regulatory approval. Because of the risk that products in development will not receive regulatory approval, we generally do not recognize any contingent payments that would be due to us until regulatory approval. Discontinued Operations We review the presentation of planned or completed business dispositions in the condensed consolidated financial statements based on the available information and events that have occurred. The review consists of evaluating whether the business meets the definition of a component for which the operations and cash flows are clearly distinguishable from the other components of the business and, if so, whether it is anticipated that after the disposal the cash flows of the component would be eliminated from continuing operations and whether the disposition represents a strategic shift that has a major effect on operations and financial results. Planned or completed business dispositions are presented as discontinued operations when all the criteria described above are met. We determined that the zaltenibart Transaction with Novo Nordisk did not meet the above criteria. As such, we recorded the gain on sale of zaltenibart in Other Income in our condensed consolidated statement of operations and comprehensive loss for the year ended December 31, 2025. On December 23, 2021, we closed on an Asset Purchase Agreement (the “Asset Purchase Agreement”) with Rayner Surgical Inc. (“Rayner”) for the sale of our commercial product OMIDRIA, which we record as an OMIDRIA contract asset on our condensed consolidated balance sheet. As a result of the divestiture, the results of OMIDRIA activities are classified as discontinued operations in our condensed consolidated statement of operations and comprehensive income (loss) and excluded from continuing operations for all periods presented. We have rights to receive future royalties from Rayner on OMIDRIA net sales at royalty rates that vary based on geography and certain regulatory contingencies. Therefore, future OMIDRIA royalties are treated as variable consideration. The sale of OMIDRIA qualified as an asset sale under GAAP. To measure the OMIDRIA contract royalty asset, we use the expected value approach, which is the sum of the discounted probability-weighted royalty payments we would receive using a range of potential outcomes, to the extent that it is probable that a significant reversal in the amount of cumulative income recognized will not occur. All U.S. royalties received from Rayner through December 31, 2031 are remitted by Rayner to an escrow account established by Omeros, from which payments are made to DRI Healthcare Acquisition LP (“DRI”) and are entirely pass-through in nature to the Company. These payments comprise interest expense, with the remainder treated as a reduction of the OMIDRIA royalty obligation. The amount recorded in discontinued operations in future periods will reflect interest earned on the outstanding OMIDRIA contract royalty asset at 11.0% and any amounts we receive that are different from the expected royalties. The OMIDRIA contract royalty asset is re-measured quarterly using the expected value approach, which incorporates actual results and future expectations. (For further details see “Note 7 — Discontinued Operations —Sale of OMIDRIA”).
Royalty Obligation Policy [Policy Text Block]	OMIDRIA Royalty Obligation On September 30, 2022, we sold to DRI a portion of our future OMIDRIA royalty receipts for a purchase price of $125.0 million and recorded an OMIDRIA Royalty Obligation for the same amount. On February 1, 2024, DRI purchased our remaining U.S. OMIDRIA royalty receipts through December 31, 2031 for $115.5 million in cash under an Amended and Restated Royalty Purchase Agreement (the “Amendment”). The Amendment eliminated the previously existing annual caps on royalty payments and provides that DRI receives all royalties on U.S. net sales of OMIDRIA payable between January 1, 2024 and December 31, 2031. We accounted for the Amendment as a modification of our existing debt from DRI. The OMIDRIA royalty obligation is valued based on our estimates of future OMIDRIA royalties and is amortized through December 31, 2031. To the extent our estimates of future royalties differ materially from the previous estimates, we will adjust for future OMIDRIA royalties to the present value of the revised estimated cash flows, discounted at the implied effective interest rate of 10.27% utilizing the cumulative catch-up method. We record interest expense as a component within continuing operations. Any such remeasurement adjustment is recognized as non-cash interest expense within continuing operations (see “Note 8 - OMIDRIA Royalty Obligation”).
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and Cash Equivalents, Short-Term Investments and Restricted Investments Cash and cash equivalents include highly liquid instruments with a maturity of three months or less on the date of purchase, which can be easily converted into cash without a significant impact on their value. Short-term investment securities are classified as held-to-maturity, except for money market funds, which are classified as available-for-sale. Investments classified as available-for-sale are measured at fair value. Investments classified as held-to-maturity are carried at cost. Amortization, accretion, interest, and dividends, realized gains and losses and declines in value judged to be other-than-temporary are included within other income. The cost of securities sold is based on the specific-identification method. Investments with maturities of less than one year, or those for which management intends to use the investments to fund current operations, are included in current assets. We evaluate whether an investment is other-than-temporarily impaired based on the specific facts and circumstances. Factors that are considered in determining whether an other-than-temporary decline in value has occurred include: the market value of the security in relation to its cost basis; the financial condition of the investee; and the intent and ability to retain the investment for a sufficient period of time to allow for recovery in the market value of the investment. Restricted investments held in money-market funds include security deposits on our office lease. Investment income, which is included as a component of other income, consists primarily of interest earned.
Accounts Receivable [Policy Text Block]	Receivables Receivables relates primarily to sales of YARTEMLEA to wholesalers and include estimated chargebacks and product returns that are expected to be settled through reductions in receivables, royalties receivable from Rayner on sales of OMIDRIA and receivables from Novo Nordisk for work performed under the Transition Services Agreement. Considering the nature of our receivables, including that trade receivables are primarily due from a limited number of customers, we recorded no material allowance for expected credit losses as of March 31, 2026 and December 31, 2025, respectively.
Property, Plant, and Equipment [Policy Text Block]	Property and Equipment, Net Property and equipment are stated at cost, and depreciation is calculated using the straight-line method over the estimated useful life of the assets, which is generally between three and ten years. Expenditures for repairs and maintenance are expensed as incurred.
Inventory, Policy [Policy Text Block]	Inventory Inventory is stated at the lower of cost or market determined on a specific identification basis in a manner that approximates the first-in, first-out (FIFO) method. Costs include amounts related to third-party manufacturing, transportation and internal labor and overhead. Capitalization of costs as inventory begins when regulatory approval of the product candidate is reasonably assured in the U.S. or the EU. We expense inventory costs related to product candidates as research and development expenses prior to receiving regulatory approval in the applicable territory. Inventory is reduced to net realizable value for excess and obsolete inventories based on forecasted demand.
Debt, Policy [Policy Text Block]	Debt The Company accounts for its convertible debt at carrying value, net of applicable discounts, premiums and debt issuance costs. These instruments are recognized as a single liability on the condensed consolidated balance sheets unless specific features require treatment under separate accounting guidance. Debt issuance costs, which include legal, accounting, and underwriting fees directly attributable to the financing, are presented as a direct deduction from the carrying amount of the convertible debt. These costs and any original issue discounts are amortized to interest expense over the contractual term of the debt using the effective interest method. The Company classifies convertible debt as long-term or current based on the remaining maturity and the status of the conversion features at the balance sheet date. If the holders of the debt possess the right to convert the instrument into shares of the Company’s common stock within one year of the balance sheet date, or if the debt is otherwise callable, the respectivecarrying value of the converted debt is classified as current. The Company performs a periodic evaluation of the conversion conditions to ensure proper classification and to determine if the debt should be measured based on its settlement value. Upon conversion, the carrying value of the debt, including any unamortized costs, is typically reclassified to stockholders’ equity, and no gain or loss is recognized unless the conversion includes an inducement. In February 2026, we repaid in full the remaining $17.1 million principal balance outstanding on our 2026 Notes upon maturity. On November 25, 2025, concurrent with the closing of the sale of zaltenibart to Novo Nordisk under the APLA, the Company repaid in full the $67.1 million principal balance outstanding under the Company’s Credit and Guarantee Agreement with certain funds managed by Athyrium Capital Management, LP and certain funds managed by Highbridge Capital Management, LLC, as lenders (the “Term Loan”). As of March 31, 2026, the Company has outstanding one series of convertible notes, which mature on June 15, 2029 (the “2029 Notes”) with an outstanding principal balance of $70.8 million. (For further details, see “Note 6 – Debt”).
Derivatives, Policy [Policy Text Block]	Embedded Derivatives We account for convertible instruments in accordance with ASC 470-20, Debt with Conversion and Other Options, when we determine that embedded conversion features do not require bifurcation from the host instrument. We account for convertible instruments (when we have determined that the embedded conversion options should be bifurcated from their host instruments) in accordance with ASC 815 – Derivative and Hedge Accounting (“ASC 815”). Under ASC 815, proceeds received upon the issuance of the hybrid contract are allocated between the fair value of the notes and the fair value of the derivative. The derivative is subsequently marked-to-market at each reporting date based on current fair value, with the changes in fair value reported in the condensed consolidated statements of operations and comprehensive loss. The embedded derivative on our 2029 Notes represents the conversion feature and interest make-whole feature available to holders of the 2029 Notes allowing them to convert the notes into cash, common stock and/or a combination thereof. The embedded derivative on our Term Loan was eliminated upon repayment on November 25, 2025. (For further details, see “Note 4 – Fair Value Measurements” and “Note 6 – Debt”).
Lessee, Leases [Policy Text Block]	Right-of-Use Assets and Related Lease Liabilities We record operating leases as right-of-use assets and recognize the related lease liabilities equal to the fair value of the lease payments using our incremental borrowing rate when the implicit rate in the lease agreement is not readily available. We recognize variable lease payments when incurred. Costs associated with operating lease assets are recognized on a straight-line basis within operating expenses over the term of the lease. We record finance lease obligations as a component of property and equipment and amortize these assets within operating expenses on a straight-line basis to their residual values over the shorter of the term of the underlying lease or the estimated useful life of the equipment. The interest component of finance lease obligations is included in interest expense and recognized using the effective interest method over the lease term. We account for leases with initial terms of 12 months or less as an operating expense.
Stockholders' Equity, Policy [Policy Text Block]	Common Stock Repurchases We have repurchased shares of our common stock from time to time under authorization made by our Board of Directors. Under applicable Washington State law, repurchased shares are retired and not presented separately as treasury stock in the condensed consolidated financial statements.
Concentration Risk, Credit Risk, Policy [Policy Text Block]	Financial Instruments and Concentrations of Credit Risk Cash and cash equivalents, receivables, accounts payable and accrued liabilities, which are recorded at invoiced amount or cost, approximate fair value based on the short-term nature of these financial instruments. The fair value of short-term investments is based on quoted market prices. Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash and cash equivalents, short-term investments and receivables. Cash and cash equivalents are held by financial institutions and are federally insured up to certain limits. At times, our cash and cash equivalents balance held at a financial institution may exceed the federally insured limits. To limit the credit risk, we invest our excess cash in high-quality securities such as money market mutual funds, certificates of deposit and U.S. treasury bills.
New Accounting Pronouncements, Policy [Policy Text Block]	Recent Accounting Pronouncements In November 2024, the Financial Accounting Standards Board (“FASB”) issued ASU 2024-03, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expense (“ASU 2024-03”), requiring public entities to disclose additional information about specific expense categories in the notes to the financial statements on an interim and annual basis. ASU 2024-03 is effective for fiscal years beginning after December 15, 2026, and for interim periods beginning after December 15, 2027, with early adoption permitted. The Company is currently evaluating the impact of adopting ASU 2024-03 on its consolidated financial statements. In December 2025, the FASB issued ASU 2025-10, Government Grants (Topic 832): Accounting for Government Grants Received by Business Entities (“ASU 2025-10”), which establishes authoritative guidance on the recognition, measurement, presentation, and disclosure of government grants. Under ASU 2025-10, government grants are recognized when it is probable that the entity will both comply with the conditions of the grant and the grant will be received. The ASU provides specific accounting models for grants related to assets and grants related to income, including options to recognize government grants as deferred income or as a reduction of the asset’s cost basis. The ASU also requires enhanced disclosures regarding the nature of government grants, significant terms and conditions, accounting policies applied, and amounts recognized in the financial statements. ASU 2025-10 is effective for fiscal years beginning after December 15, 2028, including interim periods within those fiscal years, with early adoption permitted. The Company is currently evaluating the impact of adopting ASU 2025-10 on its consolidated financial statements. In December 2025, the FASB issued ASU 2025-11, Interim Reporting (Topic 270): Narrow-Scope Improvements (“ASU 2025-11”), which clarifies the guidance in Topic 270 to improve the consistency of interim financial reporting. The ASU provides a comprehensive list of required interim disclosures and introduces a disclosure principle requiring entities to disclose events since the end of the last annual reporting period that have a material impact on the entity. ASU 2025-11 is effective for fiscal years beginning after December 15, 2027, including interim periods within those fiscal years, with early adoption permitted. The Company is currently evaluating the impact of adopting ASU 2025-11 on its consolidated financial statements.

Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2026

Segment Reporting, Policy [Policy Text Block]

Segment Reporting

We operate in one business segment focusing on the research, discovery, development and commercialization of small-molecule and protein therapeutics targeting immunologic diseases, including complement-mediated diseases and cancers related to dysfunction of the immune system, as well as addictive and compulsive disorders. The Company defines its operating segment based on internally reported financial information that is regularly used by the Chief Operating Decision Maker (“CODM”) to analyze performance, make decisions and allocate resources. The Company’s CODM is our Chief Executive Officer. For the three months ended March 31, 2026, the Company has identified one operating and reporting segment. The CODM reviews net income (loss) and expenses reported on the condensed consolidated statement of operations and comprehensive income (loss). The measurement of segment assets is reported on the condensed consolidated balance sheet as total consolidated assets. All long-lived assets are held in the U.S. Our segment net income (loss) aligns with our condensed consolidated statement of operations and comprehensive income (loss).

Revenue [Policy Text Block]

Revenue Recognition

When we enter into a customer contract, we perform the following five steps: (i) identify the contract with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) we satisfy a performance obligation.

Product Sales, Net

We generally recognize revenue from product sales when the product is delivered to our wholesalers and title to the product is transferred, upon which we have satisfied our performance obligations. Fulfillment activities by the wholesalers are not considered to be a separate performance obligation. Product revenue is recorded net of variable consideration, including wholesaler distribution fees, chargebacks, returns and discounts. We estimate variable consideration using the expected value approach. This estimate is based on several factors, including: historical return rates, expiration date by product and estimated levels of inventory in the wholesale channel. Since there is often a timing lag between the product sale and the settlement of accruals relating to these programs, our net product revenue may incorporate revisions of accruals for several periods. We include such estimates in the transaction price only to the extent that it is probable that a significant reversal of revenue will not occur when the uncertainty associated with the variable consideration is subsequently resolved.

Given the limited commercialization history of YARTEMLEA, our estimates of variable consideration require judgment and are subject to change as additional data becomes available. We recognize adjustments to net product revenue in the period in which changes in estimates become known.

Chargebacks

Chargebacks represent discounts provided to eligible covered entities under government programs, including the 340B Drug Pricing Program (“340B”) and the Medicaid Drug Rebate Program (“Medicaid”). In addition, we are subject to pricing obligations under our Federal Supply Schedule agreement with the U.S. government (the “FSS Agreement”), which establishes maximum prices for sales to certain federal agencies and may give rise to additional discounts and rebates. Chargebacks are recorded as a reduction of gross product revenue at the time of sale. Reserves for chargebacks are generally recorded as reductions of accounts receivable, while reserves for Medicaid rebates and patient co-pay assistance, if applicable, are recorded as accrued liabilities.

Chargeback estimates are based on statutory pricing requirements applicable to the 340B program and expected utilization by covered entities. Given the limited commercial history of our recently launched product, these estimates require significant judgment, including assumptions related to future utilization patterns and channel inventory. Estimates are reassessed at each reporting period and adjusted as necessary based on actual experience, changes in 340B utilization, and other relevant factors.

In addition to 340B chargebacks and Medicaid rebates, we maintain programs that may result in additional variable consideration, including a patient co-pay assistance program. There was no activity under the Medicaid and co-pay assistance program during the three months ended March 31, 2026, and, accordingly, no material related reductions to gross product revenue were recorded. We will continue to evaluate these programs as utilization evolves and will recognize the related reductions to revenue in the period in which they occur.

Distribution Fees and Return Allowances

We pay distribution fees to wholesalers for services they perform on our behalf. These fees are calculated based on the wholesalers’ average acquisition cost of purchases of YARTEMLEA, exclusive of any chargebacks. We estimate these amounts at the time of sale to the wholesaler and record them as a reduction in product sales in the same period the related revenue is recognized.

We allow for the return of product up to 12 months past its expiration date or for product that is damaged. In estimating product returns, we take into consideration our return experience to date, the remaining shelf-life of product we have previously sold, inventory in the wholesale channel, and our expectation that product is typically not held by health care providers based on the frequency of their reorders. There were no product returns in the three months ended March 31, 2026. Due to the ordering patterns associated with transplant centers and the extended shelf life of YARTEMLEA, returns are expected to be limited; however, our estimates may change as commercial experience matures.

Cost of Goods and Service [Policy Text Block]

Cost of Product Sales

Cost of product sales includes third-party manufacturing, royalties based on net product sales, and other costs directly related to the production and distribution of YARTEMLEA. We expensed as research and development expense all costs associated with the manufacture of YARTEMLEA produced prior to FDA approval. As a result, the cost basis of inventory available for sale at the time of commercialization was minimal, and cost of product sales is correspondingly low during the initial period following launch. Following FDA approval, we capitalize direct manufacturing costs as inventory and recognize these amounts in cost of product sales when the related inventory is sold. Accordingly, cost of product sales and gross margin during the initial periods following commercialization may not be indicative of future periods as we begin capitalizing and expensing post‑approval manufacturing costs.

Research and Development Expense, Policy [Policy Text Block]

Research and Development

Research and development expenses are comprised primarily of contracted research and development activities, clinical trial study and manufacturing costs prior to approval; consulting services; contract milestones; materials and supplies; costs for personnel, including salaries, benefits, and stock-based compensation; depreciation; an allocation of our occupancy costs; and other expenses incurred to sustain our overall research and development programs. Advance payments for goods or services that will be used for future research and development activities are deferred and then recognized as an expense as the related goods are delivered or the services are performed. All other research and development costs are expensed as incurred.

Selling, General and Administrative Expenses, Policy [Policy Text Block]

Selling, General and Administrative

Selling, general and administrative expenses are comprised primarily of marketing expenses; professional and legal services; patent costs; and salaries, benefits, and stock-based compensation costs for marketing and other personnel not directly engaged in research and development. Additionally, selling, general and administrative expenses include depreciation, an allocation of our occupancy costs, and other general corporate expenses. Advertising costs are expensed as incurred.

Share-Based Payment Arrangement [Policy Text Block]

Stock-Based Compensation

Stock-based compensation expense is recognized for all share-based payments, including grants of stock option awards and restricted stock units based on estimated fair values. The fair value of our stock is calculated using the Black-Scholes option-pricing model, which requires assumptions around volatility, forfeiture rates, risk-free interest rate and expected term. Compensation expense is recognized over the requisite service periods, which is generally the vesting period, using the straight-line method. Forfeiture expense is estimated at the time of grant and revised in subsequent periods if actual forfeitures differ from those estimates.

Income Tax, Policy [Policy Text Block]

Income Taxes

Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their tax basis. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be recovered or settled. We recognize the effect of income tax positions only if those positions are more likely than not to be sustained upon an examination by the relevant taxing authority. A valuation allowance is established when it is more likely than not that the deferred tax assets will not be realized.

Discontinued Operations, Policy [Policy Text Block]

Asset Sale Transactions

The Company evaluates transactions involving the sale of our compounds, products or drug programs to determine whether such arrangements represent a sale of a business or a sale of a nonfinancial asset. Transactions that do not meet the definition of a business are accounted for as the sale of a nonfinancial asset under Accounting Standards Codification (“ASC”) 610‑20, Other Income—Gains and Losses from the Derecognition of Nonfinancial Assets.

Upon transfer of control of the compound, product or drug program asset to a counterparty, the Company recognizes consideration received. Any excess of consideration over the carrying value of the asset sold is recognized as a gain in the condensed consolidated statements of operations.

Potential Milestone Income

The APLA with Novo Nordisk includes variable consideration in the form of milestone payments that are contingent upon the achievement of specified development, regulatory or commercialization events. The Company applies the variable consideration and constraint guidance in ASC 606, Revenue from Contracts with Customers, by analogy. At contract inception and throughout the term of the arrangement, the Company assesses whether the achievement of each milestone is probable and estimates variable consideration using the most likely amount method. Contingent milestone payments are excluded from the transaction price until the related milestone is achieved and it is probable that a significant reversal of cumulative revenue recognized will not occur.

Amounts are included in the transaction price only to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. The Company re-evaluates the transaction price at each reporting period, including the estimated variable consideration and the application of the constraint, to reflect changes in circumstances. Factors considered in these evaluations include the clinical or technical complexity of the milestone, the stage of development, and the risk of regulatory approval. Because of the risk that products in development will not receive regulatory approval, we generally do not recognize any contingent payments that would be due to us until regulatory approval.

Discontinued Operations

We review the presentation of planned or completed business dispositions in the condensed consolidated financial statements based on the available information and events that have occurred. The review consists of evaluating whether the business meets the definition of a component for which the operations and cash flows are clearly distinguishable from the other components of the business and, if so, whether it is anticipated that after the disposal the cash flows of the component would be eliminated from continuing operations and whether the disposition represents a strategic shift that has a major effect on operations and financial results. Planned or completed business dispositions are presented as discontinued operations when all the criteria described above are met.

We determined that the zaltenibart Transaction with Novo Nordisk did not meet the above criteria. As such, we recorded the gain on sale of zaltenibart in Other Income in our condensed consolidated statement of operations and comprehensive loss for the year ended December 31, 2025.

On December 23, 2021, we closed on an Asset Purchase Agreement (the “Asset Purchase Agreement”) with Rayner Surgical Inc. (“Rayner”) for the sale of our commercial product OMIDRIA, which we record as an OMIDRIA contract asset on our condensed consolidated balance sheet. As a result of the divestiture, the results of OMIDRIA activities are classified as discontinued operations in our condensed consolidated statement of operations and comprehensive income (loss) and excluded from continuing operations for all periods presented. We have rights to receive future royalties from Rayner on OMIDRIA net sales at royalty rates that vary based on geography and certain regulatory contingencies. Therefore, future OMIDRIA royalties are treated as variable consideration. The sale of OMIDRIA qualified as an asset sale under GAAP. To measure the OMIDRIA contract royalty asset, we use the expected value approach, which is the sum of the discounted probability-weighted royalty payments we would receive using a range of potential outcomes, to the extent that it is probable that a significant reversal in the amount of cumulative income recognized will not occur.

All U.S. royalties received from Rayner through December 31, 2031 are remitted by Rayner to an escrow account established by Omeros, from which payments are made to DRI Healthcare Acquisition LP (“DRI”) and are entirely pass-through in nature to the Company. These payments comprise interest expense, with the remainder treated as a reduction of the OMIDRIA royalty obligation. The amount recorded in discontinued operations in future periods will reflect interest earned on the outstanding OMIDRIA contract royalty asset at 11.0% and any amounts we receive that are different from the expected royalties. The OMIDRIA contract royalty asset is re-measured quarterly using the expected value approach, which incorporates actual results and future expectations. (For further details see “Note 7 — Discontinued Operations —Sale of OMIDRIA”).

Royalty Obligation Policy [Policy Text Block]

OMIDRIA Royalty Obligation

On September 30, 2022, we sold to DRI a portion of our future OMIDRIA royalty receipts for a purchase price of $125.0 million and recorded an OMIDRIA Royalty Obligation for the same amount. On February 1, 2024, DRI purchased our remaining U.S. OMIDRIA royalty receipts through December 31, 2031 for $115.5 million in cash under an Amended and Restated Royalty Purchase Agreement (the “Amendment”). The Amendment eliminated the previously existing annual caps on royalty payments and provides that DRI receives all royalties on U.S. net sales of OMIDRIA payable between January 1, 2024 and December 31, 2031. We accounted for the Amendment as a modification of our existing debt from DRI. The OMIDRIA royalty obligation is valued based on our estimates of future OMIDRIA royalties and is amortized through December 31, 2031.

To the extent our estimates of future royalties differ materially from the previous estimates, we will adjust for future OMIDRIA royalties to the present value of the revised estimated cash flows, discounted at the implied effective interest rate of 10.27% utilizing the cumulative catch-up method. We record interest expense as a component within continuing operations. Any such remeasurement adjustment is recognized as non-cash interest expense within continuing operations (see “Note 8 - OMIDRIA Royalty Obligation”).

Cash and Cash Equivalents, Policy [Policy Text Block]

Cash and Cash Equivalents, Short-Term Investments and Restricted Investments

Cash and cash equivalents include highly liquid instruments with a maturity of three months or less on the date of purchase, which can be easily converted into cash without a significant impact on their value. Short-term investment securities are classified as held-to-maturity, except for money market funds, which are classified as available-for-sale. Investments classified as available-for-sale are measured at fair value. Investments classified as held-to-maturity are carried at cost. Amortization, accretion, interest, and dividends, realized gains and losses and declines in value judged to be other-than-temporary are included within other income.

The cost of securities sold is based on the specific-identification method. Investments with maturities of less than one year, or those for which management intends to use the investments to fund current operations, are included in current assets. We evaluate whether an investment is other-than-temporarily impaired based on the specific facts and circumstances. Factors that are considered in determining whether an other-than-temporary decline in value has occurred include: the market value of the security in relation to its cost basis; the financial condition of the investee; and the intent and ability to retain the investment for a sufficient period of time to allow for recovery in the market value of the investment. Restricted investments held in money-market funds include security deposits on our office lease.

Investment income, which is included as a component of other income, consists primarily of interest earned.

Accounts Receivable [Policy Text Block]

Receivables

Receivables relates primarily to sales of YARTEMLEA to wholesalers and include estimated chargebacks and product returns that are expected to be settled through reductions in receivables, royalties receivable from Rayner on sales of OMIDRIA and receivables from Novo Nordisk for work performed under the Transition Services Agreement. Considering the nature of our receivables, including that trade receivables are primarily due from a limited number of customers, we recorded no material allowance for expected credit losses as of March 31, 2026 and December 31, 2025, respectively.

Property, Plant, and Equipment [Policy Text Block]

Property and Equipment, Net

Property and equipment are stated at cost, and depreciation is calculated using the straight-line method over the estimated useful life of the assets, which is generally between three and ten years. Expenditures for repairs and maintenance are expensed as incurred.

Inventory, Policy [Policy Text Block]

Inventory

Inventory is stated at the lower of cost or market determined on a specific identification basis in a manner that approximates the first-in, first-out (FIFO) method. Costs include amounts related to third-party manufacturing, transportation and internal labor and overhead. Capitalization of costs as inventory begins when regulatory approval of the product candidate is reasonably assured in the U.S. or the EU. We expense inventory costs related to product candidates as research and development expenses prior to receiving regulatory approval in the applicable territory. Inventory is reduced to net realizable value for excess and obsolete inventories based on forecasted demand.

Debt, Policy [Policy Text Block]

Debt

The Company accounts for its convertible debt at carrying value, net of applicable discounts, premiums and debt issuance costs. These instruments are recognized as a single liability on the condensed consolidated balance sheets unless specific features require treatment under separate accounting guidance. Debt issuance costs, which include legal, accounting, and underwriting fees directly attributable to the financing, are presented as a direct deduction from the carrying amount of the convertible debt. These costs and any original issue discounts are amortized to interest expense over the contractual term of the debt using the effective interest method.

The Company classifies convertible debt as long-term or current based on the remaining maturity and the status of the conversion features at the balance sheet date. If the holders of the debt possess the right to convert the instrument into shares of the Company’s common stock within one year of the balance sheet date, or if the debt is otherwise callable, the respectivecarrying value of the converted debt is classified as current. The Company performs a periodic evaluation of the conversion conditions to ensure proper classification and to determine if the debt should be measured based on its settlement value. Upon conversion, the carrying value of the debt, including any unamortized costs, is typically reclassified to stockholders’ equity, and no gain or loss is recognized unless the conversion includes an inducement.

In February 2026, we repaid in full the remaining $17.1 million principal balance outstanding on our 2026 Notes upon maturity. On November 25, 2025, concurrent with the closing of the sale of zaltenibart to Novo Nordisk under the APLA, the Company repaid in full the $67.1 million principal balance outstanding under the Company’s Credit and Guarantee Agreement with certain funds managed by Athyrium Capital Management, LP and certain funds managed by Highbridge Capital Management, LLC, as lenders (the “Term Loan”). As of March 31, 2026, the Company has outstanding one series of convertible notes, which mature on June 15, 2029 (the “2029 Notes”) with an outstanding principal balance of $70.8 million. (For further details, see “Note 6 – Debt”).

Derivatives, Policy [Policy Text Block]

Embedded Derivatives

We account for convertible instruments in accordance with ASC 470-20, Debt with Conversion and Other Options, when we determine that embedded conversion features do not require bifurcation from the host instrument. We account for convertible instruments (when we have determined that the embedded conversion options should be bifurcated from their host instruments) in accordance with ASC 815 – Derivative and Hedge Accounting (“ASC 815”). Under ASC 815, proceeds received upon the issuance of the hybrid contract are allocated between the fair value of the notes and the fair value of the derivative. The derivative is subsequently marked-to-market at each reporting date based on current fair value, with the changes in fair value reported in the condensed consolidated statements of operations and comprehensive loss.

The embedded derivative on our 2029 Notes represents the conversion feature and interest make-whole feature available to holders of the 2029 Notes allowing them to convert the notes into cash, common stock and/or a combination thereof. The embedded derivative on our Term Loan was eliminated upon repayment on November 25, 2025. (For further details, see “Note 4 – Fair Value Measurements” and “Note 6 – Debt”).

Lessee, Leases [Policy Text Block]

Right-of-Use Assets and Related Lease Liabilities

We record operating leases as right-of-use assets and recognize the related lease liabilities equal to the fair value of the lease payments using our incremental borrowing rate when the implicit rate in the lease agreement is not readily available. We recognize variable lease payments when incurred. Costs associated with operating lease assets are recognized on a straight-line basis within operating expenses over the term of the lease.

We record finance lease obligations as a component of property and equipment and amortize these assets within operating expenses on a straight-line basis to their residual values over the shorter of the term of the underlying lease or the estimated useful life of the equipment. The interest component of finance lease obligations is included in interest expense and recognized using the effective interest method over the lease term.

We account for leases with initial terms of 12 months or less as an operating expense.

Stockholders' Equity, Policy [Policy Text Block]

Common Stock Repurchases

We have repurchased shares of our common stock from time to time under authorization made by our Board of Directors. Under applicable Washington State law, repurchased shares are retired and not presented separately as treasury stock in the condensed consolidated financial statements.

Concentration Risk, Credit Risk, Policy [Policy Text Block]

Financial Instruments and Concentrations of Credit Risk

Cash and cash equivalents, receivables, accounts payable and accrued liabilities, which are recorded at invoiced amount or cost, approximate fair value based on the short-term nature of these financial instruments. The fair value of short-term investments is based on quoted market prices. Financial instruments that potentially subject us to concentrations of credit risk consist primarily of cash and cash equivalents, short-term investments and receivables. Cash and cash equivalents are held by financial institutions and are federally insured up to certain limits. At times, our cash and cash equivalents balance held at a financial institution may exceed the federally insured limits. To limit the credit risk, we invest our excess cash in high-quality securities such as money market mutual funds, certificates of deposit and U.S. treasury bills.

New Accounting Pronouncements, Policy [Policy Text Block]

Recent Accounting Pronouncements

In November 2024, the Financial Accounting Standards Board (“FASB”) issued ASU 2024-03, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expense (“ASU 2024-03”), requiring public entities to disclose additional information about specific expense categories in the notes to the financial statements on an interim and annual basis. ASU 2024-03 is effective for fiscal years beginning after December 15, 2026, and for interim periods beginning after December 15, 2027, with early adoption permitted. The Company is currently evaluating the impact of adopting ASU 2024-03 on its consolidated financial statements.

In December 2025, the FASB issued ASU 2025-10, Government Grants (Topic 832): Accounting for Government Grants Received by Business Entities (“ASU 2025-10”), which establishes authoritative guidance on the recognition, measurement, presentation, and disclosure of government grants. Under ASU 2025-10, government grants are recognized when it is probable that the entity will both comply with the conditions of the grant and the grant will be received. The ASU provides specific accounting models for grants related to assets and grants related to income, including options to recognize government grants as deferred income or as a reduction of the asset’s cost basis. The ASU also requires enhanced disclosures regarding the nature of government grants, significant terms and conditions, accounting policies applied, and amounts recognized in the financial statements. ASU 2025-10 is effective for fiscal years beginning after December 15, 2028, including interim periods within those fiscal years, with early adoption permitted. The Company is currently evaluating the impact of adopting ASU 2025-10 on its consolidated financial statements.

In December 2025, the FASB issued ASU 2025-11, Interim Reporting (Topic 270): Narrow-Scope Improvements (“ASU 2025-11”), which clarifies the guidance in Topic 270 to improve the consistency of interim financial reporting. The ASU provides a comprehensive list of required interim disclosures and introduces a disclosure principle requiring entities to disclose events since the end of the last annual reporting period that have a material impact on the entity. ASU 2025-11 is effective for fiscal years beginning after December 15, 2027, including interim periods within those fiscal years, with early adoption permitted. The Company is currently evaluating the impact of adopting ASU 2025-11 on its consolidated financial statements.