Warfarin is used to decrease the tendency for thrombosis, or as secondary prophylaxis (prevention of further episodes) in those individuals who have already formed a blood clot (thrombus). Warfarin (Coumadin, Jantoven) is a prescription drug used to treat DVTs, reduction of pulmonary embolism and atrial fibrillation, and prevent strokes and heart attacks. The Basics of Warfarin Drug Interactions Before we go over the “Fab Five” that make up the “Oh Shit” list, let’s review the kinetics of warfarin to help us understand why these drug interactions occur in the first place. For starters, warfarin is a substrate of CYP2C9 (major), 1A2 (minor), and 3A4 (minor). Now that’s a lot of CYPs. Please try a new search and if you still don't find what you're looking for, visit our Contact Us page for helpful links and contact information. Donate today to help end heart disease and stroke for everyone. NHS information about the medicine warfarin, including what it's used for, who can use it, how to use it and side effects. Find patient medical information for Warfarin on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings Warfarin is an anticoagulant used to prevent heart attacks, strokes, and blood clots. Learn about side effects, interactions and indications. Warfarin is used to prevent or treat blood clots, including deep venous thrombosis or pulmonary embolism. It is also used for blood clots that may be caused by certain heart conditions, open-heart surgery, or after a heart attack. Warfarin is used to treat blood clots and/or to prevent new clots from forming in your body. Learn about side effects, drug interactions, dosages, warnings, and more. What Is Warfarin? Warfarin (Coumadin® and Jantoven®) is an anticoagulant medication or “blood thinner” you take to prevent and treat blood clots that can lead to a stroke or heart attack. Warfarin slows down your blood’s ability to clot.