In a meta-analysis of 171,215 individuals without established atherosclerotic cardiovascular disease (ASCVD), Aspirin use decreased myocardial infarction at the expense of raised rates of major bleeding. Among persons without ASCVD, stratified by statin usage across various ASCVD risks, researchers sought to assess the effects of Aspirin.

Randomized controlled studies of Aspirin without ASCVD with a follow-up of ≥1 year were chosen after a database search. Relative and absolute risks were calculated for cardiovascular outcomes, severe bleeding, and fatality during 5 years using random-effects models. Estimation of absolute risk differences was done on the assumption that ASCVD risks and statin usage had constant relative risks (RRs). The baseline risks were calculated utilizing data from: (1) ASCEND (A Study of Cardiovascular Events in Diabetes) trial, and (2) Cholesterol Treatment Trialists Collaboration.

Compared to the control group, Aspirin decreased myocardial infarction (RR: 0.85) but increased severe bleeding (RR: 1.48) in 16 studies (n = 171,215; median age, 64 years). Mortality was not decreased by Aspirin. Reduction in bleeding and myocardial infarction risks were linked to statin use vs. no statin use; ASCVD risk was inversely correlated with bleeding and myocardial infarction risk.

Proportional to the hazard of ASCVD at baseline, Aspirin decreased myocardial infarction (very high risk: forty-nine events as monotherapy or thirty-seven events with a statin; very low risk: three events as monotherapy or one event with a statin). Also, it elevated fatal bleeding (very high risk: ninety-eight events as monotherapy or ninety-four events with a statin; very low risk: twenty-one events as monotherapy or twenty events with a statin) for every 10,000 adults. Concomitant statin was promising in individuals without ASCVD.

For all the levels of ASCVD risk, the absolute risk of significant bleeding with Aspirin exceeded the absolute myocardial infarction advantages.  Hence, the use of “cardio” Aspirin carries a significant bleeding risk that exceeds its potentially protective benefits. These results might have implications for use of Aspirin in those already on statins for ASCVD primary prevention.