Anticoagulants (often called "blood thinners") prevent the formation of new thrombi and the extension of existing clots. They are among the highest-risk medications in clinical practice because the same property that makes them therapeutic also creates a continuous risk of life-threatening bleeding. Anticoagulants are prescribed to treat and prevent venous thromboembolism (deep vein thrombosis and pulmonary embolism), to reduce stroke risk in atrial fibrillation, to manage acute coronary syndrome, to protect mechanical heart valves, and to provide coverage after surgery or prolonged immobility. A point that learners often miss: anticoagulants do not dissolve clots that already exist — that is the job of thrombolytics (for example, alteplase). Anticoagulants simply stop the clotting cascade from building more clot while the body's own fibrinolytic system gradually breaks down what is already present. This lesson covers the four major classes the registered nurse must know cold: - Unfractionated heparin (UFH): given IV or subcutaneously, monitored by aPTT, reversed by protamine sulfate. - Low molecular weight heparin (LMWH) such as enoxaparin: subcutaneous only, predictable dosing, anti-Xa monitoring reserved for special populations. - Warfarin: oral,...