Greens and garlic and my favorite chamomile tea, lots of herbs, etc. effect how Coumadin works and would be awesome to see an article for folks like me. Answer: Coumadin, also known as warfarin, is an anticoagulant (blood thinning') medication that's usually used to prevent or treat blood clots. Warfarin works by slowing down vitamin K activity and increases the time it takes for your blood to clot. Making significant changes in the amounts of vitamin K you consume in a short period can mess with your warfarin dosage, so it's important to speak with your doctor about the foods you eat.