Anticoagulants are various active substances that prevent or reduce blood clotting. Anticoagulants can be administered orally as tablets or by injection. They are used preventively (as prophylaxis) or therapeutically (e.g. in case of thrombosis or embolism). The most important side effect of anticoagulants is an increased risk of bleeding. The Swiss Atlas of Healthcare shows the most frequently used anticoagulation drugs dispensed by outpatient care providers.