To summarize, warfarin is the drug mostly commonly reported to interact with supplements. However, reporting of interactions is sporadic and sometimes contradictory. For example, Ginseng may increase the clearance of warfarin, but trial evidence is conflicting. Co-enzyme Q10 and Ginkgo biloba may not interfere with warfarin activity significantly, but further study is necessary. St. John's wort likely increases hepatic clearance of warfarin and phenprocoumon, thereby decreasing the anti-coagulant effect of these coumarins.