An anticoagulant is a medicine that stops the blood from clotting. "Anti" means against and "coagulant" means to thicken into a gel or solid. Sometimes the medicines are referred to as "blood thinners."

There are a few different kinds of anticoagulants; vitamin K antagonists, heparins, and newer agents like the direct thrombin inhibitors and direct factor Xa inhibitors. They are mainly used to prevent or treat deep vein thrombosis, pulmonary embolism, and strokes.