Why Is OMER Stock Falling Today?

European regulators issued a negative opinion on Yartemlea, Omeros’ therapy for hematopoietic stem cell transplant-associated thrombotic microangiopathy.
In this photo illustration, the Omeros Corporation logo is seen displayed on a smartphone screen. (Photo Illustration by Thomas Fuller/SOPA Images/LightRocket via Getty Images)
In this photo illustration, the Omeros Corporation logo is seen displayed on a smartphone screen. (Photo Illustration by Thomas Fuller/SOPA Images/LightRocket via Getty Images)
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Ahmed Farhath·Stocktwits
Published Jun 26, 2026   |   8:33 AM EDT
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  • Yartemlea is Omeros’ therapy to treat a rare, life-threatening complication that can happen after a bone marrow or stem cell transplant.
  • The European Medicines Agency said the study data Omeros submitted did not contain sufficient evidence of Yartemlea's effectiveness.
  • The regulator has given Omeros 15 days to request a re-examination of the opinion.

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Shares of Omeros Corporation (OMER) were down on Friday after the biopharmaceutical company’s therapy to treat a rare, fatal complication following a bone marrow or stem cell transplant received an unfavorable recommendation from European medical regulators, throwing a wrench in its commercialization efforts in the region.

At the time of writing, OMER stock was down 18%, on track for its lowest level in more than seven months if losses hold, and among the top ten trending tickers on Stocktwits.

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European Regulator Rejects Omeros’ Yartemlea

According to the European Medicines Agency’s (EMA) Committee for Medicinal Products for Human Use’s website, Narsoplimab, which is sold under the commercial name Yartemlea, received a negative opinion. The regulator refused to give the company’s therapy marketing approval in the region.

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The agency said the study data Omeros submitted did not contain sufficient evidence of Yartemlea's effectiveness.

“The main study supporting the application did not compare Yartemlea with placebo or another treatment. Participants were also taking other medications in addition to Yartemlea. Because of this, it was not possible to determine whether the observed benefits were due to Yartemlea, other medicines taken, or other reasons,” EMA said in its detailed report.

Omeros Drug: Additional Study Concerns Flagged

The regulator also raised questions about how the study was conducted, including
changes made during the study, how effectiveness was measured, and how the dose was chosen, among other things.

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Moreover, it determined that the company submitted insufficient data for approving its proposed dosage recommendation for children.

EMA has given Omeros 15 days to request a re-examination of the opinion. Yartemlea is a therapy for adults and children from two years of age with hematopoietic stem cell transplant-associated thrombotic microangiopathy. It is currently approved by the FDA in the U.S.

What Retail Traders Think Of OMER Stock

On Stocktwits, retail sentiment toward OMER turned ‘neutral’ from ‘bearish’ over the last 24 hours.

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OMER stock is down 38% so far this year, but has more than tripled in value over the past 12 months.

For updates and corrections, email newsroom[at]stocktwits[dot]com.

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