To date, there have been few systematic studies of the antiplatelet and/or anticoagulant effects of natural products. According to the Natural Medicines Comprehensive Database, approximately 180 dietary supplements have the potential to interact with warfarin, and more than 120 may interact with aspirin, clopidogrel, and dipyridamole. These include anise and dong quai (anticoagulant effects); omega 3-fatty acids in fish oil, ajoene in garlic, ginger, ginko, and vitamin E (antiplatelet properties); fucus (heparin-like activity); danshen (antithrombin III-like activity and anticoagulant bioavailability); and St. John's Wort and American Ginseng (interference with drug metabolism). Other supplements, such as high doses of vitamin E (vitamin K antagonist activity), alfalfa (high-vitamin K content), and coenzyme Q10 (vitamin K-like activity), may affect blood clotting, which is dependent on vitamin K. Studies are needed to understand the role of various dietary supplements in thrombosis and their interactions with standard anticoagulants and antiplatelet drugs.