By irreversibly inhibiting platelet function, aspirin reduces risk of atherothrombosis but also increases risk of bleeding, particularly in the gas- Aspirin is well established for secondary prevention of ASCVDS4.6-12 and is widely rec- ommended for this indication.S4.6-13 However, in primary prevention, aspirin use is more controversial. Because persons without prior ASCVD are inherently less likely to have future ASCVD events than are those with a prior history, it is more challenging for clinicians and patients to balance benefits and harms of prophylactic aspirin for primary prevention. This uncertainty is re- flected in international guidelines, where, for example, aspirin is not recommended in European guidelines for primary ASCVD preventionS4.6-13 but is recommended in prior US guidelines for selected primary prevention for adults who have elevated risk of ASCVD based on tradi- tional risk factors.S4.6-14,S4.6-15 Adding to this controversy are more recently conducted primary-prevention trials that, in contrast to older trials,S4.6-12 have shown less overall benefit of prophylactic aspirin alongside coad- ministration of contemporary ASCVD preventive treat- ments, such as evidence-based hypertension and cho- Recommendation-Specific Supportive Text 1. 