A European regulatory panel has rejected Biogen Alzheimer's disease medication, potentially putting the drug's chances in jeopardy. The drug is already facing a delayed rollout in the United States.

Before the bell, the Cambridge, Massachusetts-based company's stock was down 3.6% after the panel's unfavorable vote on Aduhelm. Up until Tuesday's close, they had dropped about 25% in the previous three months.

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The EMA will evaluate the panel's suggestion, which it is not obligated to follow but normally does.

"Given the existing data and controversy attached to the drug, we see no reason why there would be a divergence (in EMA's decision)," Wedbush analyst laura chico said.

Despite contradictory results and a vote against approval by an independent panel of the US Food and Medication Administration, the drug was approved by US regulators earlier this year.

On Monday, Biogen announced that Alfred Sandrock, the company's research leader who oversaw the development of its Alzheimer's disease medicine, was retiring after a 23-year tenure, a decision that analysts described as abrupt.

Aduhelm, the first new treatment for Alzheimer's disease in over two decades, has had limited uptake in the United States as hospitals and health insurers await a decision on whether the drug will be covered by the US government.

The EMA's advisory group determines the regulator's therapy, vaccination, or device recommendations.

At a meeting in December, the Committee for Medicinal Products for Human Use will issue a final opinion on Biogen's Aduhelm, according to the firm.

The European Commission, the executive body of the European Union, makes the ultimate and formal decision after the EMA has authorized or refused a product. This decision usually matches what the EMA has indicated.