 Warfarin , also known by the brand names Coumadin among others , is an anticoagulant normally used in the prevention of thrombosis and thromboembolism , the formation of blood clots in the blood vessels and their migration elsewhere in the body , respectively . It was initially introduced in 1948 as a pesticide against rats and mice , and is still used for this purpose. Hinweis: Warfarin ist eine Medizin. Warfarin is a vitamin K antagonist that works by interfering with the synthesis of vitamin K-dependent coagulation factors. Warfarin is a vitamin K antagonist, which means it prevents the body from producing