Herb-drug interactions: review and assessment of report reliability.

AIMS: The aim of this systematic review was to assess the published clinical evidence on interactions between herbal and conventional drugs. METHODS: Four electronic databases were searched for case reports, case series or clinical trials of such interactions. The data were extracted and validated using a scoring system for interaction probability. RESULTS: One hundred and eight cases of suspected interactions were found. 68.5% were classified as 'unable to be evaluated', 13% as 'well-documented' and 18.5% as 'possible' interactions. Warfarin was the most common drug (18 cases) and St John's wort the most common herb (54 cases) involved. CONCLUSION: Herb-drug interactions undoubtedly do occur and may put individuals at risk. However our present knowledge is incomplete and more research is urgently needed.