Aspirin may be a promising alternative for those who can't take long-term anticoagulant drugs that prevent clots from reoccurring in the veins, according to a new paper in Circulation.

In a combined analysis of two similar independent studies, 1,224 patients who received 100 mg of aspirin a day to treat blood clots were monitored for at least two years. In the International Collaboration of Aspirin Trials for Recurrent Venous Thromboembolism or INSPIRE analysis, researchers found that aspirin reduced the risk of recurring blood clots by up to 42 percent.

Venous thromboembolism (VTE) are blood clots in veins. The blood clot can occur in the deep veins of the legs (deep vein thrombosis) and can break apart and travel to the lungs, where they block off arteries in the lungs (pulmonary embolism).

According to researchers, without treatment, people who have blood clots in their veins with no obvious cause have on average a 10 percent risk of another clot within the first year and a 5 percent risk per year thereafter.

"The treatment is warfarin or a newer anticoagulant usually given for at least six to 12 months to prevent a further blood clot," said John Simes, M.D., lead author of study and director of the National Health and Medical Research Council Trials Centre and professor at the University of Sydney in Australia. "However, these people continue to be at risk."

Co-author Cecilia Becattini, M.D., added, "Aspirin does not require laboratory monitoring, and is associated with about a 10-fold lower incidence of bleeding compared with oral anticoagulants. We are convinced that it will be an alternative for extended prevention of venous thromboembolism after 6