What were the results of the Women's Health Study?
The Women's Health Study found a 17% reduction in the risk of stroke (RR, 0.76; 95% CI, 0.63 0.93; P=0.009) and a nonsignificant increase in the risk of gastrointestinal hemorrhage requiring transfusion (RR, 1.17; 95% CI, 0.91-1.50; P=0.13) in the combined primary end point among women. Overall average stroke rates were 0.11% per year in aspirin-treated women and 0.13% per year in placebo-treated women (RR, 0.02% per year; number needed to treat, 5000). An important adverse outcome, gastrointestinal hemorrhage requiring transfusion, was more frequent in the aspirin group (increase, 0.01% per year; number needed to harm, 10000).