Do homeopathic medicines provoke adverse effects? A systematic review

OBJECTIVE: To evaluate the safety of homeopathic medicines by critically appraising reports of adverse effects published in English from 1970 to 1995. METHOD: Systematic review on information regarding adverse effects of homeopathic medicines identified using electronic databases, hand searching, searching reference lists, reviewing the bibliography of trials, and other relevant articles, contacting homeopathic pharmaceutical companies and drug regulatory agencies in UK and USA, and by communicating with experts in homeopathy. RESULTS: The mean incidence of adverse effects of homeopathic medicines was greater than placebo in controlled clinical trials (9.4/6.1) but effects were minor, transient and comparable. There was a large incidence of pathogenetic effects in healthy volunteers taking homeopathic medicines but the methodological quality of these studies was generally low. Anecdotal reports of adverse effects in homeopathic publications were not well documented and mainly reported aggravation of current symptoms. Case reports in conventional medical journals pointed more to adverse effects of mislabelled 'homeopathic products' than to true homeopathic medicines. CONCLUSIONS: Homeopathic medicines in high dilutions, prescribed by trained professionals, are probably safe and unlikely to provoke severe adverse reactions. It is difficult to draw definite conclusions due to the low methodological quality of reports claiming possible adverse effects of homeopathic medicines.