In addition to the US, Biogen has also asked regulators in Australia, Brazil, Canada, the European Union, Japan, and Switzerland to review the drug.
US approval is a critical win for a company that relies on Aduhelm to offset stalled or declining sales of its other products. Competitors introduced generics of Biogen's multiple sclerosis drug Tecfidera last year, missing hundreds of millions of dollars in revenue from its best-selling product to date.
The approval changes Biogen "completely," said Brian Skorney, an analyst at Robert W. Baird & Company, who expects the drug will have sales of $ 7.5 billion in 2025, "he said, opening it "A bit of Pandora's box" in terms of pricing and reimbursement.
While only patients with a slight cognitive decline were included in the clinical trials, the F.D.A. approved the drug for anyone with Alzheimer's disease, a much broader group of patients than many experts expected.
How lucrative the drug will be for Biogen depends on how many patients it can reach – and under what circumstances and how long insurers are willing to pay for it.
Dr. Steve Miller, the chief clinical officer of insurer Cigna, said Monday he expected his company and most of his colleagues would only pay for the drug for patients with mild cognitive symptoms and above-average levels of the protein amyloid in their brains.
"There is simply no data that will benefit more advanced patients," he said.
Dr. Miller said he was disappointed that the F.D.A. had made so many patients suitable. "You leave the difficult decision about who should be covered to the individual payers," he said.