Eighteen RCTs (n=5,269) were included in the review. Where reported, Jadad scores ranged from 2 to 5 points with six RCTs scoring 4 or 5 points. Six RCTs could not be assessed for quality. Duration of follow-up ranged from 10 days to 6.7 years.
There was no overall statistically significant difference in the composite outcome of nonfatal myocardial infarction, nonfatal stroke and cardiovascular death between the aspirin and placebo or control groups (RR 0.88, 95% CI: 0.76, 1.04, 18 RCTs). There was a significantly lower incidence of nonfatal stroke in the aspirin groups (RR 0.66, 95% CI: 0.47, 0.94, 18 RCTs), but there were no statistically significant differences between the groups for any other secondary efficacy outcome. There was no statistically significant difference between the groups in incidence of major bleeding, but this was not formally assessed in many included RCTs.
Results of subgroup and sensitivity analyses were also reported. No evidence of significant publication bias was detected.