Warfarin is an anticoagulant used as a medication under several brand names including Coumadin. While the drug is described as a "blood thinner", it does not reduce viscosity but rather inhibits coagulation. Accordingly, it is commonly used to prevent blood clots in the circulatory system such as deep vein thrombosis and pulmonary embolism, and to protect against stroke in people who have atrial fibrillation, valvular heart disease, or artificial heart valves. Less commonly, it is used following ST-segment elevation myocardial infarction (STEMI) and orthopedic surgery. It is usually taken by mouth, but may also be administered intravenously.