Warfarin is an anticoagulant drug used to prevent blood clots. It is a synthetic derivative of dicoumarol that was developed by the Wisconsin Alumni Research Foundation. Warfarin works by inhibiting vitamin K epoxide reductase and preventing the recycling of vitamin K, which is necessary for blood clotting. It exists as a white crystalline powder and is available in oral tablet forms of 1mg, 3mg, and 5mg doses. Warfarin is used to prevent embolisms in conditions like atrial fibrillation and after inserting prosthetic heart valves, but has contraindications like peptic ulcers and should be used cautiously in hepatic or renal impairment.