Interactions of warfarin with garlic, ginger, ginkgo, or ginseng: Nature of the evidence

OBJECTIVE: To review and characterize the evidence describing potential interactions between warfarin and garlic, ginger, ginkgo, or ginseng. DATA SOURCES: Searches of MEDLINE (1966-1999), other bibliographic databases, several abstracting services, and tertiary references were conducted. STUDY SELECTION AND DATA EXTRACTION: Articles were examined by each author, and additional citations were obtained from the references of these articles. Preference was given to English-language articles of human studies. DATA SYNTHESIS: Evidence is lacking for an interaction of warfarin with garlic or ginger. Once case report associates ginseng use with decreased warfarin-maintained anticoagulation effect. Another case report links concomitant use of ginkgo and warfarin with the development of intracerebral hemorrhage. Hemorrhage and bleeding tendencies were noted in four cases with ginkgo use and in three cases with garlic; in none of these cases were patients receiving warfarin. CONCLUSIONS: The true risks of these interactions and effects are difficult to characterize due to the limited number and nature of existing reports.