Five RCTs (55,580 participants) were included. The results of one study were only used in the combined vascular events outcome.
There was no significant heterogeneity between the studies.
For nonfatal MI there was a statistically-significant risk reduction of 32% associated with aspirin therapy (RR 0.68, 95% CI: 0.59, 0.79).
There was no significant effect of aspirin use on nonfatal stroke (RR 1.06, 95% CI: 0.87, 1.29) or ischaemic stroke (RR 0.97, 95% CI: 0.77, 1.22); there was a suggestion that aspirin use increased the risk of haemorrhagic stroke (RR 1.56, 95% CI: 0.99, 2.46).
There was a statistically-significant reduction in the risk of any important vascular event in the aspirin-treated group (RR 0.85, 95% CI: 0.79, 0.93). For vascular deaths there was no significant reduction in risk (RR 0.98, 95% CI: 0.85, 1.12).