The benefits of low-dose aspirin for the secondary prevention of cardiovascular disease are well established. Its value for the primary prevention of symptomatic cardiovascular disease, however, remains controversial, because the risk of bleeding may outweigh the benefits. Of particular concern is intracranial hemorrhage, which is strongly associated with a high mortality risk and poorer health over a lifetime.

A systematic review and meta-analysis of randomized clinical trials was undertaken to determine whether low-dose aspirin increases the risk of intracranial hemorrhage in people who don't have symptomatic cardiovascular disease. This analysis included 13 randomized clinical trials, for a total of 134,446 enrollees, that compared the use of low-dose aspirin (100 mg/day or less) with control (placebo or no aspirin). Trials that included patients with symptomatic cardiovascular disease were excluded, as were those that examined the use of other antithrombotic agents.

Pooled results showed that low-dose aspirin was associated with a higher risk of any intracranial bleeding compared with control. In terms of absolute risk, for every 1,000 people treated with low-dose aspirin instead of control, an additional two intracranial hemorrhages could occur. Low-dose aspirin was also associated with an increased risk of subdural or extradural hemorrhage. Subgroup analysis showed that the increased bleeding risk associated with low-dose aspirin was greatest in Asian populations and in populations with a low body mass index (less than 25 kg/m2).

Although these increases in risk were modest, they are clinically relevant according to the authors, who conclude that the adverse outcomes of intracranial hemorrhage may outweigh the benefits of low-dose aspirin if it's given universally. They also note that both studies of Asian-only populations were conducted in Japan and thus may not be fully representative of other Asian populations.

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