ADAPTABLE is a pragmatic clinical trial in which 20,000 patients who are at high risk for ischemic events will be randomly assigned in a 1:1 ratio to receive an aspirin dose of 81 mg/day vs. 325 mg/day. Study participants will be enrolled over 24 months. Maximum follow-up will be 30 months. The purpose of the study is to identify the optimal dose of aspirin for secondary prevention in patients with Atherosclerotic cardiovascular disease (ASCVD). The primary endpoint is a composite of all-cause death, hospitalization for MI, or hospitalization for stroke. The primary safety endpoint is hospitalization for major bleeding with an associated blood product transfusion.