Definition: Anticoagulants are drugs that prevent blood clots in the body, typically to treat conditions such as atrial fibrillation, congestive heart failure, or certain types of cancer. Definition: Anticoagulants are substances used to prevent or control blood clots, especially in the veins and arteries. They do this by stopping a chemical reaction called coagulation that can cause a clot to form. Common anticoagulants include vitamin K inhibitors like warfarin for bleeding conditions such as atrial fibrillation and congestive heart failure, and antiplatelet drugs such as aspirin, clopidogrel, and prasugrel. Anticoagulants can also help with other medical conditions by preventing blood clots in people at increased risk. They are typically prescribed to treat a wide range of conditions but should be used under the supervision of a healthcare professional.