Blood thinner drugs, also known as anticoagulants, are used for their properties of preventing the coagulation of blood, which can block arteries. Anticoagulants are used in treating thrombosis (inappropriate blood coagulation in the blood vessels), pulmonary embolism and strokes. Blood thinner drugs act by antagonizing the effect of vitamin K or activating antithrombin III (a substance that stops the clotting of blood). They can either take time to have an effect (the case of warfarin – Coumadin, which takes 48 to 72 hours to be fully effective), or they can be immediately effective, such as heparin (injectable anticoagulant). Direct thrombin inhibitors such as dabigatran or argatroban might be used.