Coumadin is mainly used to reduce the risk of blood clots in the body. It is usually prescribed to people with problems such as atrial fibrillation, those who have had heart valve surgery, or who have had clots in the legs (deep vein thrombosis) or lungs (pulmonary embolism). Coumadin is also sometimes used to prevent recurrence of clots in people who have had them in the past.
Coumadin works by inhibiting blood clotting factors, which keeps the blood fluid and helps reduce the chances of blood vessels becoming blocked.