Potentially dangerous blood clotting disorders can be prevented by administering low doses of a blood thinning drug, research has found.
The finding gives doctors a safer long-term treatment for deep vein thrombosis - which is thought to be a particular risk for long distance air travellers and others who spend long periods in cramped conditions.
Deep vein thrombosis occurs when a blood clot forms, usually in the veins of the leg, and causes pain and cramps.
If part of the clot breaks off and travels to the lungs, it can cause a potentially fatal blockage known as a pulmonary embolism.
People who develop one clot have a high risk for developing another.
The drug warfarin, which thins the blood, is designed to reduce the risk of clotting.
But doctors have been reluctant to use the drug over long periods because it can cause unwanted and potentially dangerous bleeding.
The new study, by a team from Brigham and Women's
Hospital in Boston, found that a lower-than-normal dose
prevents the clots from reappearing.
The study of 508 volunteers over four years was halted
early because the results were so impressive - people given low-dose warfarin developed up to 80% fewer clots than patients given a dummy treatment.
Lead researcher Dr Paul Ridker said: "Because low-intensity warfarin is both safe and highly effective, and inexpensive, this is a real 'win win win' for our patients."
The research is published in the New England Journal of Medicine.