In July 2023, the US Food and Drug Administration (FDA) provided full approval for an amyloid-β–directed antibody, lecanemab (Leqembi), for treating Alzheimer disease. The prescribing information states that treatment, which is administered as an intravenous infusion, should be initiated in patients with mild cognitive impairment or the mild dementia stage of the disease, which is the population in which the treatment was studied in clinical trials. Lecanemab is the second monoclonal antibody targeting β-amyloid protein to be approved; the first was aducanumab (Aduhelm) in 2021. The FDA approved lecanemab via its accelerated approval program in January 2023 based solely on the decline in β-amyloid as estimated on positron emission tomography scans in the brains of patients taking the drug compared with placebo. The agency granted full approval of lecanemab based on clinical efficacy data from a clinical trial with 1795 participants.1 Advocacy groups were pressuring the US Centers for Medicare & Medicaid Services to pay for the drug.