An anticoagulant is a medication that reduces the blood’s ability to clot, lowering the risk of dangerous clot formation within blood vessels. Anticoagulants are sometimes called blood thinners, although they do not literally thin the blood; they interrupt part of the clotting cascade so that clots form more slowly or not at all.
Anticoagulants are used to prevent and treat a range of conditions including [atrial fibrillation](/glossary/atrial-fibrillation/) (where clots can form in the left atrial appendage and cause stroke), deep vein thrombosis, pulmonary embolism, and left ventricular thrombus (a clot forming inside a weakened heart). They are also used in people with mechanical heart valves and in some other conditions where clot risk is elevated.
The main classes of anticoagulant used in the UK are:
– **Warfarin:** a vitamin K antagonist that has been used for decades. Effective but requires regular blood test monitoring (INR) to keep the dose within the therapeutic range, as the effect is influenced by diet and other medications.
– **Direct oral anticoagulants (DOACs):** including apixaban, rivaroxaban, edoxaban, and dabigatran. These target specific clotting factors directly, do not require routine monitoring, and are now the preferred choice for most patients with atrial fibrillation.
– **Low molecular weight heparins (LMWH):** injectable anticoagulants (such as enoxaparin) used in hospital and sometimes at home for shorter-term treatment.
Anticoagulants increase the risk of bleeding, and patients taking them should be aware of signs of unusual bleeding (such as blood in urine or stools, prolonged nosebleeds, or unexplained bruising). Any procedure, dental treatment, or new medication should be discussed with a healthcare professional to ensure the anticoagulant is managed safely. See also: [Anticoagulation](/glossary/anticoagulation/).
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