Biogen will stop developing its Alzheimer's treatment Aduhelm, a drug once seen as a potential blockbuster before stumbling soon after its launch a couple years ago.

The drugmaker said Wednesday that it will end a study of the drug needed for full approval from the Food and Drug Administration, and it will stop sales of Aduhelm.

Patients taking doses of Aduhelm available through the commercial market can continue until November. A company representative said there are about 2,500 people worldwide taking Aduhelm.

Biogen said it will turn its focus more to other treatments for Alzheimer's, a fatal, mind-robbing disease. The company also is helping Japanese drugmaker Eisai sell another Alzheimer's treatment, Leqembi, which already has full FDA approval.

Leqembi is the first medicine that's been convincingly shown to slow the cognitive decline caused by Alzheimer's disease, though only modestly. Regulators have approved it for patients with mild dementia and other symptoms caused by early Alzheimer's.

Aduhelm was the first new Alzheimer's disease drug introduced in nearly two decades. The FDA granted accelerated approval for it in 2021. But regulators required an additional study before they would consider full approval.

Initially priced at $56,000 a year, analysts predicted it would quickly become a blockbuster drug that would generate billions for Biogen.

But doctors were hesitant to prescribe the intravenous drug, given weak evidence that the drug slows Alzheimer's. Insurers have blocked or restricted coverage, and the federal government's Medicare program imposed strict limits on who could get it.

That proved especially challenging for Biogen because most U.S. Alzheimer's patients are old enough to qualify for the federal program, which covers patients age 65 and older.

The drug wound up generating millions, not billions, in quarterly sales for Biogen, and the company announced in 2022 that it would largely shut down marketing of Aduhelm.

Last year, Biogen started an unsuccessful search for outside financing or partners to help with Aduhelm. That was done as part of a review the company did of its research and development program.

Biogen said it had considered during that review the time and investment that would be required for that additional study and likely advancements in the field before Aduhelm received full approval.

The company said it would book a charge of about $60 million in its fourth quarter for shutting down the Aduhelm program.

Shares of Cambridge, Massachusetts-based Biogen Inc. climbed more than $4 to $251.72 Wednesday morning while the Standard & Poor's 500 index slipped.