Context.— Aspirin has been widely used to prevent
myocardial infarction and ischemic stroke but some studies have
suggested it increases risk of hemorrhagic stroke.
Objective.— To estimate the risk of hemorrhagic stroke
associated with aspirin treatment.
Data Sources.— Studies were retrieved using MEDLINE (search
terms, aspirin, cerebrovascular disorders, and
stroke), bibliographies of the articles retrieved, and the
authors' reference files.
Study Selection.— All trials published in English-language
journals before July 1997 in which participants were randomized to
aspirin or a control treatment for at least 1 month and in which the
incidence of stroke subtype was reported.
Data Extraction.— Information on country of origin, sample
size, duration, study design, aspirin dosage, participant
characteristics, and outcomes was abstracted independently by 2 authors
who used a standardized protocol.
Data Synthesis.— Data from 16 trials with 55,462
participants and 108 hemorrhagic stroke cases were analyzed. The mean
dosage of aspirin was 273 mg/d and mean duration of treatment was 37
months. Aspirin use was associated with an absolute risk reduction in
myocardial infarction of 137 events per 10,000 persons (95%
confidence interval [CI], 107-167; P<.001) and in ischemic
stroke, a reduction of 39 events per 10,000 persons (95% CI,
17-61; P<.001). However, aspirin treatment was also
associated with an absolute risk increase in hemorrhagic stroke of 12
events per 10,000 persons (95% CI, 5-20; P<.001).
This risk did not differ by participant or study design
Conclusions.— These results indicate that aspirin therapy
increases the risk of hemorrhagic stroke. However, the overall benefit
of aspirin use on myocardial infarction and ischemic stroke may
outweigh its adverse effects on risk of hemorrhagic stroke in most