Seven RCTs met the inclusion criteria, but data for meta-analysis was only available for five studies (7,384 participants).
Study quality was high. Appropriate methods of randomisation were used in all studies. Three studies were double blind. Two open label studies included blind assessment or outcomes. Drop-outs were reported in all studies.
Compared to control, aspirin had no statistically significant effect on major adverse cardiovascular events (p for heterogeneity >0.9, three studies), fatal or nonfatal myocardial infarction (I2=64%, three studies), nonfatal myocardial infarction (two studies), fatal or nonfatal stroke (I2=29%, three studies), fatal stroke (two studies), cardiovascular mortality (I2=39%, four studies) and all-cause mortality (p for heterogeneity = 0.75, four studies).
Using fixed-effect analysis, aspirin was associated with an increased risk of major bleeding (RR 2.51, 95% CI 1.11 to 5.70; two studies). This result was not statistically significant with a random-effects model (RR 3.02, 95% CI 0.48 to 18.86, I2=66%). There was no statistically significant effect on gastrointestinal bleeding (I2=72%, three studies).