The experimental Alzheimer’s drug lecanemab, hailed after it slowed patients’ cognitive decline in a clinical trial, may have contributed to the death in June of a patient in the study, STAT has learned.

One investigator on the study flagged the death, noting it came after the patient experienced bleeding in the brain, and concluded it was related to the drug, according to documents obtained by STAT. Eisai, the drugmaker behind lecanemab, disagreed, pointing to other possible factors, including a series of setbacks in preceding months — multiple falls, a heart attack, a respiratory infection, and mini-stroke-like events.

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Though still under investigation, the death suggests that new medicines to treat Alzheimer’s, like medicines to treat anything else, will come with their own side effects and costs. It also raises the importance of waiting for the full lecanemab data before drawing conclusions based on the positive press release put out by Eisai and its partner Biogen last month.

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