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, although more potent poisons such as brodifacoum have since been developed. In the early 1950s, warfarin was found to be effective and relatively safe for preventing thrombosis and thromboembolism in many disorders. It was approved for use as a medication in 1954, and has remained popular ever since. Warfarin is the most widely prescribed oral anticoagulant drug in North America.