AbstractAlthough inflammation is strongly associated with frailty, whether medications that lower inflammation decrease frailty is unclear and randomized trial evidence is scant. We sought to test whether canakinumab, a therapeutic monoclonal antibody that inhibits IL‐1β and reduces C‐reactive protein (CRP), can lower frailty risk. This was a post hoc analysis of the Canakinumab ANti‐inflammatory Thrombosis Outcome Study (CANTOS), a randomized double‐blind placebo‐controlled trial of 10,061 stable postmyocardial infarction patients randomized to subcutaneous canakinumab once every 3 months. Incident frailty was measured using a 34‐item cumulative‐deficit Frailty Index (FI). Time‐to‐event analysis using intent to treat. A total of 9942 CANTOS participants had data to calculate a baseline FI. Median age was 61 (IQR 54–68); 74% were male, 12% Asian, 3% Black, 80% White, and 16% Hispanic/Latino. At baseline, mean FI score was 0.12 and 13% were frail using a cutoff of 0.2. Over 5 years, 1080 participants (12.5%) became frail and mean FI scores increased to 0.14. There was no effect on frailty incidence according to randomization to any canakinumab dose versus placebo over time, HR 1.03 (0.91–1.17), p = 0.63. Results were similar using phenotypic frailty. Additionally, the primary findings of CANTOS in terms of canakinumab‐associated cardiovascular event reduction were unchanged in analyses stratified by baseline frailty. In conclusion, among stable adult patients with atherosclerosis, random allocation to interleukin‐1b inhibition with canakinumab versus placebo did not lower risk of incident frailty over 5 years. More randomized data are needed to understand the role of targeted anti‐inflammatory medications for frailty prevention in older adults.