Harvard Heart Letter

Aspirin may prevent blood clots in the legs from recurring

People who develop blood clots in their legs—a condition called venous thromboembolism—must take warfarin (Coumadin) for several months or longer to prevent another clot from forming and possibly traveling to the lungs, with deadly results. Yet warfarin can cause unwanted bleeding and requires regular blood testing. As a result, no one wants to be on this treatment forever. The question is, what else might they do to reduce their risk for another blood clot if they stop taking warfarin?

Now the combined results of two compatible studies have determined that a low dose of aspirin (100 mg per day) may be an effective substitute for long-term use of warfarin. Both studies examined people who had developed a clot in the legs for unknown reasons. In both studies, the clots were dissolved with heparin, and treatment with warfarin followed for up to three months. Then warfarin was discontinued, and the study participants were given either daily low-dose aspirin or placebo (sugar pill). Compared with placebo, aspirin reduced the rate of recurrent clots by one-third, and helped prevent strokes, heart attacks, and other undesirable consequences, with a very low risk of bleeding. The researchers concluded that low-dose aspirin would be a reasonable option for long-term clot prevention in people who suffer a first clot for unknown reasons.

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