tokens: Pooled data from trials comparing antithrombotic treatment with placebo have shown that warfarin reduces the risk of stroke by 62 %, and that aspirin alone reduces the risk by 22 %. Overall , in high - risk patients , warfarin is superior to aspirin in preventing strokes , with a relative risk reduction of 36 %. Ximelagatran , an oral direct thrombin inhibitor , was found to be as efficient as vitamin K antagonist drugs in the prevention of embolic events , but has been recently withdrawn because of abnormal liver function tests .