Omeros Corporation Reports Third Quarter 2020 Financial Results SEATTLE, WA

Omeros Corporation Reports Third Quarter 2020 Financial Results

SEATTLE, WA - November 9, 2020 - Omeros Corporation (Nasdaq: OMER), a commercial-stage biopharmaceutical company committed to discovering, developing and commercializing small-molecule and protein therapeutics for large-market as well as orphan indications targeting inflammation, complement-mediated diseases, disorders of the central nervous system and immune-related diseases, including cancers, today announced recent highlights and developments as well as financial results for the third quarter ended September 30, 2020, which include:

"The final clinical study results for narsoplimab in the treatment of transplant-associated TMA speak for themselves. The non-clinical and CMC sections of the BLA are under review by FDA, and the clinical sections, which will be submitted next week, are complete, comprehensive and compelling," said Gregory A. Demopulos, M.D., Omeros' chairman and chief executive officer. "In anticipation of priority review, our team is readying for a successful commercial launch.

Beyond TA-TMA and its Phase 3 trials in IgA nephropathy and aHUS, narsoplimab is increasingly recognized as a likely answer to severe COVID-19. Our complement franchise continues expanding with our MASP-3 inhibitor OMS906 on course and marching through its Phase 1 program. Confident that OMIDRIA qualifies for separate payment from CMS, we expect that the drug will increasingly support our unique portfolio of complement inhibitors and the rest of our exciting pipeline programs. Developing a life-saving drug is a rare opportunity, and all of us at Omeros are energized and inspired by the patients - children and adults - who are alive today because of our team's efforts."

Third Quarter and Recent Developments

For the third quarter of 2020, OMIDRIA revenues were $26.1 million, down from $29.9 million for the same period in 2019 and up from $13.5 million for the second quarter of 2020. The decrease compared to the third quarter of 2019 was due to an $8.7 million deduction as a reserve for product returns related to the expiration of pass-through reimbursement on October 1, 2020.

Total costs and expenses for the third quarter of 2020 were $51.5 million compared to $41.0 million for the same period in 2019. The increase reflects a fee payable under a technology license agreement related to Omeros' MASP-3 program and increased pre-commercialization marketing activities for narsoplimab. Selling, general and administrative expenses were $19.8 million in the third quarter of 2020, compared to $16.9 million in the corresponding period in 2019.

For the three months ended September 30, 2020, Omeros reported a net loss of $38.5 million, or $0.66 per share, compared to a net loss of $16.5 million, or $0.33 per share, for the same period in 2019. On a non-GAAP basis, adjusted net loss for the three months ended September 30, 2020 was $19.9 million, or $0.34 per share, after excluding non-cash expenses of $13.6 million, or $0.23 per share, and a technology access fee of $5.0 million, or $0.09 per share. Both net loss and adjusted net loss include the $8.7 million deduction in the third quarter of 2020 for the return reserve.

As of September 30, 2020, Omeros had $153.5 million of cash, cash equivalents and short-term investments available for operations and accounts receivable of $37.4 million.

During the third quarter, Omeros issued approximately $225.0 million aggregate principal amount 5.25% convertible senior notes due February 2026 (the 2026 Notes). Concurrently, Omeros repurchased $115.0 million aggregate principal amount of previously outstanding 6.25% convertible senior notes due November 2023. Omeros recorded a $13.4 million non-cash loss on early extinguishment of debt and a $7.9 million non-cash income tax benefit associated with these transactions. Omeros also entered into capped call contracts associated with the 2026 Notes that cover, subject to anti-dilution adjustments that may not match those applicable to the conversion price of the 2026 Notes, the number of shares of Omeros' common stock underlying the 2026 Notes when Omeros' common stock is trading between the initial conversion price of approximately $18.49 and the $26.10 cap price.

In August, Omeros sold 6.9 million shares in an underwritten public offering and received $93.7 million in net proceeds from the offering.

About Omeros Corporation

Omeros is a commercial-stage biopharmaceutical company committed to discovering, developing and commercializing small-molecule and protein therapeutics for large-market and orphan indications targeting inflammation, complement-mediated diseases, disorders of the central nervous system and immune-related diseases, including cancers. Its commercial product OMIDRIA (phenylephrine and ketorolac intraocular solution) 1%/0.3% continues to gain market share in cataract surgery. Omeros' lead MASP-2 inhibitor narsoplimab targets the lectin pathway of complement and is the subject of a rolling biologics license application for hematopoietic stem cell transplant-associated thrombotic microangiopathy. Narsoplimab is also in multiple late-stage clinical development programs focused on other complement-mediated disorders, including IgA nephropathy, atypical hemolytic uremic syndrome and COVID-19. Omeros' MASP-3

inhibitor OMS906, which targets the complement system's alternative pathway, recently entered the clinic, and the company's PDE7 inhibitor OMS527 has successfully completed Phase 1. Omeros' pipeline holds a diverse group of preclinical programs including a novel antibody-generating technology and a proprietary GPCR platform through which it controls 54 new GPCR drug targets and their corresponding compounds. One of these novel targets, GPR174, modulates a new cancer immunity axis recently discovered by Omeros, and the company is advancing small-molecule GPR174 inhibitors.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934, which are subject to the "safe harbor" created by those sections for such statements. All statements other than statements of historical fact are forward-looking statements, which are often indicated by terms such as "anticipate," "believe," "could," "estimate," "expect," "goal," "intend," "likely," "look forward to," "may," "objective," "plan," "potential," "predict," "project," "should," "slate," "target," "will," "would" and similar expressions and variations thereof. Forward-looking statements are based on management's beliefs and assumptions and on information available to management only as of the date of this press release. Omeros' actual results could differ materially from those anticipated in these forward-looking statements for many reasons, including, without limitation, risks associated with product commercialization and commercial operations, unproven preclinical and clinical development activities, the impact of COVID-19 on our business, financial condition and results of operations, regulatory oversight, changes in reimbursement and payment policies by government and commercial payers or the application of such policies, intellectual property claims, competitive developments, litigation, and the risks, uncertainties and other factors described under the heading "Risk Factors" in the company's Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on March 2, 2020, as supplemented by our Quarterly Reports on Form 10-Q filed with the SEC and subsequent filings with the SEC. Given these risks, uncertainties and other factors, you should not place undue reliance on these forward-looking statements, and the company assumes no obligation to update these forward-looking statements, whether as a result of new information, future events or otherwise, except as required by applicable law.

Non-GAAP Information

This press release includes financial measures that are not calculated in accordance with U.S. generally accepted accounting principles (GAAP). To supplement Omeros' consolidated financial statements presented in accordance with GAAP, Omeros is presenting adjusted net loss and adjusted net loss per share, which are non-GAAP financial measures. Adjusted net loss consists of GAAP net loss excluding non-cash expenses and a technology access fee.

Omeros believes that the presentation of these non-GAAP financial measures provides important supplemental information to investors regarding financial trends relating to Omeros' results of operations and facilitates comparisons of the company's core operating performance against prior periods. The non-GAAP measures should be considered supplemental to, and not a substitute for or superior to, financial measures calculated in accordance with GAAP because non-GAAP financial measures used in this press release have limitations in that they do not reflect all costs associated with the operations of Omeros' business. In addition, these measures may be different from, and therefore not comparable to, similarly titled measures used by other companies. The accompanying table provides more detail on the GAAP financial measures that are most directly comparable to the non-GAAP financial measures described above and the related reconciliations between these financial measures.

Jennifer Cook Williams

Cook Williams Communications, Inc.

Investor and Media Relations

UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS

(In thousands, except share and per share data)

UNAUDITED CONSOLIDATED BALANCE SHEET DATA

ADJUSTED NET LOSS AND ADJUSTED NET LOSS PER SHARE

TO NET LOSS AND EARNINGS PER SHARE

(In thousands, except per share data)