On 29 August, the U.S. Food and Drug Administration approved a once-weekly subcutaneous autoinjector formulation of lecanemab for maintenance dosing after an initial 18-month intravenous course in adults with mild cognitive impairment or mild dementia due to Alzheimer’s disease. After 18 months of 10mg/kg IV every two weeks, patients may either continue IV at 10mg/kg once every four weeks or switch to a weekly 360mg subcutaneous injection delivered in about 15 seconds. The decision is supported by Clarity AD open-label extension sub-studies showing that switching to weekly subcutaneous maintenance preserved clinical and biomarker effects seen with continued IV dosing. Across studied doses, safety was similar to IV maintenance with a markedly lower rate of systemic reactions on the subcutaneous route (<1% vs ~26% with IV). Injection-site reactions were usually mild. Amyloid-related imaging abnormality rates on the weekly 360mg schedule were comparable to those seen with continued IV after 18 months and close to background rates reported in untreated patients. U.S. launch is planned for 6 October 2025, supplied by Eisai and Biogen.