Among those who took the combination, "the incidence of major vascular events was reduced by 11 percent, which was a highly significant result," Connolly said.

The main effect of the combination was to reduce the incidence of stroke by about a third, from 3.4 percent to 2.4 percent a year, Connolly said. The incidence of heart attacks was reduced from 0.9 percent a year to 0.7 percent a year, a result that was not statistically significant, he said.

The incidence of major bleeding, such as hemorrhaging, was higher among those taking the combination -- 2 percent a year compared with 1.27 percent among those taking aspirin alone.

"When we consider the risk for patients, combination therapy prevents 28 strokes, 17 of them disabling, and six myocardial infarctions [heart attacks] per 1,000 patients a year, at a cost of 20 major bleeds, three of which would be fatal," Connolly said.

The bottom line, he said, is that "we can reduce major vascular events, primarily strokes, with a bearable cost in bleeding."

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Editor:Yang Jie