Alpha-tocopherol × Warfarin

NIH ODS describes two routes: vitamin E inhibits platelet aggregation and antagonises vitamin K-dependent clotting factors. With anticoagulants, high doses raise bleeding risk, especially when vitamin K intake is low. The exact clinically relevant amount is not established, though it probably exceeds 400 IU per day.

Bleeding gums, nosebleeds, bruising. The risk rises in someone who eats few leafy greens and takes high-dose vitamin E on their own.

The vitamin E label advises against 400 IU a day or more in general, except in specific disorders. With warfarin, high vitamin E doses (300 mg a day or more) can prolong prothrombin time, so prothrombin time is monitored and the warfarin dose adjusted if needed (vitamin E SmPC). When vitamin E is started or stopped, check coagulation more often: the Spanish warfarin SmPC requires close coagulation control whenever a concomitant medicine is started or stopped, and the US label (FDA) asks for more frequent INR monitoring.