Placebo effect sizes in homeopathic compared to conventional drugs – a systematic review of randomised controlled trials

Abstract

It has been hypothesised that randomised, placebo-controlled clinical trials (RCTs) of classical (individualised) homeopathy often fail because placebo effects are substantially higher than in conventional medicine. To compare placebo effects in clinical trials on homeopathy to placebo effects on trials of conventional medicines. We performed a systematic literature analysis on placebo-controlled double-blind RCTs on classical homeopathy. Each trial was matched to three placebo-controlled double-blind RCTs from conventional medicine (mainly pharmacological interventions) involving the same diagnosis. Matching criteria included severity of complaints, choice of outcome parameter, and treatment duration. Outcome was measured as the percentage change of symptom scores from baseline to end of treatment in the placebo group. 35 RCTs on classical homeopathy were identified. 10 were excluded because no relevant data could be extracted, or less than three matching conventional trials could be located. In 13 matched sets the placebo effect in the homeopathic trials was larger than the average placebo effect of the conventional trials, in 12 matched sets it was lower (P=0.39). Additionally, no subgroup analysis yielded any significant difference. Placebo effects in RCTs on classical homeopathy did not appear to be larger than placebo effects in conventional medicine.