Name a common anticoagulant medication prescribed for atrial fibrillation.

Warfarin is a common anticoagulant medication prescribed for patients with atrial fibrillation due to its long-established use and effectiveness in preventing thromboembolic events, such as stroke, in these patients. Warfarin works by inhibiting vitamin K-dependent clotting factors in the liver, which decreases the blood's ability to form clots.

This medication requires regular monitoring of the International Normalized Ratio (INR) to ensure patients maintain therapeutic levels, as its anticoagulant effect can be influenced by dietary vitamin K intake and interactions with numerous other medications. Although newer anticoagulants like apixaban are now widely used, warfarin remains a standard option due to its proven efficacy, history of use, and availability.

Other options like clopidogrel are not primarily used as anticoagulants for atrial fibrillation but rather as antiplatelet agents, which can prevent clot formation in different conditions, and heparin, while an anticoagulant, is generally used for short-term management in hospital settings or specific acute scenarios rather than for long-term management of atrial fibrillation.