Several anticoagulant drugs are administered parenterally, with heparin being the most common. Heparin can be given as unfractionated heparin, by injection or infusion, or as low-molecular-weight heparin (LMWH), which is typically administered by injection. The most common side effect of heparin therapy is bleeding, which can range from minor bruising to life-threatening hemorrhages. Closely monitoring hemostatic parameters is crucial to reducing the risk of severe bleeding. Another rare but potentially serious complication of heparin use is heparin-induced thrombocytopenia, which appears as a paradoxical thrombotic condition caused by heparin-induced platelet activation. Quick recognition and prompt discontinuation of heparin are essential for managing this condition.