Anticoagulants are molecules intended to delay or prevent clotting. They make the blood more fluid and can cause bleeding. These drugs are used in the treatment and prevention of thrombosis (fixed blood clots in the venous circulation) and embolisms (mobile blood clots that can reach the pulmonary arterial circulation). There are 3 varieties of drugs belonging to anticoagulants: heparins , antivitamin K and direct oral anticoagulants (DOACs).