Signage for Eisai Co. at the company's headquarters in Tokyo, Japan, on Friday, Feb. 3, 2023. Bloomberg | Bloomberg | Getty ImagesShares of Japanese pharmaceutical giant Eisai sank Friday after the company's Alzheimer's drug was formally approved by U.S. regulators overnight, prompting questions over investor sentiment surrounding the move. Eisai shares closed 4.67% lower after paring some of its earlier losses. Leqembi is the first Alzheimer's antibody treatment to receive full FDA approval. "The odds for brain swelling and hemorrhage are far higher than any actual improvement," Espay, who launched a petition in June calling for the Alzheimer's treatment to not get full approval, told NBC News.

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Persons: Biogen, Dr, Alberto Espay, Espay, Ivan Cheung, CNBC's, Cheung Organizations: Bloomberg, Getty, U.S, . Food, Medicare, University of Cincinnati College of, NBC News, Eisai U.S Locations: Tokyo, Japan, Eisai