The U.S. Food and Drug Administration said it converted its approval of the Alzheimer's drug Leqembi to a traditional approval, allowing the medication to be more widely used.
The FDA added a black-box warning informing patients and health care providers of its safety risks.
Medicare said it would cover a significant portion of the high cost of the drug, a move which is expected to further make it available to more patients.
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Teresa Buracchio, an acting director at the FDA said a "confirmatory study verified that it is a safe and effective treatment for patients with Alzheimer's disease."
The FDA says Alzheimer's is an irreversible brain disorder that is progressive, affecting over 6.5 million Americans.
The drug's label says in rare cases Leqembi can cause "serious and life-threatening events," and also says it can lead to brain bleeding, which has been fatal in some cases.
The most common side effects of the drug have been headache, infusion-related reactions and amyloid-related imaging abnormalities, the FDA said.
Some experts on Alzheimer's say studies still haven't yielded clear data on the drug's ability to delay the erosion of memory and cognition.
Dr. Jason Karlawish of the University of Pennsylvania's Penn Memory Center told the New York Times, "Within the first few months, you may have small bleeds or swelling in your brain, which may or may not be symptomatic and if not detected in time can cause disability."
Medicare is expected to cover around 80% of the drug's $26,500 price tag.