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.