Heparin is an anticoagulant used to prevent and treat thrombosis and pulmonary embolism, and during certain procedures including dialysis. It enhances antithrombin, a protein that limits blood clotting. It prevents new clots from forming and existing clots from growing, but does not dissolve them directly.
Injectable unfractionated heparin is given intravenously or under the skin, never into a muscle. Doses are prescribed individually; clotting tests and platelet counts may be needed. Heparin gels are used locally for bruises and symptoms involving superficial veins. They are applied to intact skin and do not replace injectable treatment.
The main risk of injectable heparin is bleeding. Bruising, injection reactions and occasionally an immune-related fall in platelets can occur. This reaction can paradoxically cause new clots; any previous episode must be reported before treatment. Gels may cause local irritation or allergy and must not be applied to wounds or bleeding areas.
Seek urgent help for persistent bleeding, black stools, blood in urine, a sudden severe headache, breathlessness or a suddenly swollen, painful leg. Do not add aspirin, ibuprofen or other anticoagulants without medical approval. Inform the doctor before procedures, including dental treatment or spinal anaesthesia, and do not change the dose yourself.