Introduction: The homeopathic medicine (defined here as the use of high dilutions of active principles) is widely used in several European countries. The mechanism of action remains unclear and the reality of the efficacy of these treatments is controversial. On the initiative of the European Parliament a quantitative systematic overview of the evidence on the clinical efficacy of the homeopathic medicine has been undertaken.

Objective: To assess the efficacy of homeopathy versus placebo or no treatment.

Methods: The randomised clinical trials testing homeopathic medicine versus placebo or no treatment were identified through several ways: electronic searching on bibliographic databases such as Medline, Embase; handsearching in homeopathic journals; contacts with experts and pharmaceutical firms. Reports in all language were considered. Reading and data extraction was performed by several readers using a specifically designed summary form. Each paper was read twice by two independent readers. The statistical analysis for this meta-analysis raised very specific problems. The question addressed is broad and all trials, irrespective of the disease and the treatment must be taken into consideration. Combining the p-values is a method which can take into account the diversity found and can be used to compute an overall indicator of the efficacy. However in many trials the primary outcome was not defined, and this might have led to a potential bias because a significant result could be due to chance alone after a large number of comparisons. Finally several meta-analysis were performed grouping the trials by their methodological quality, with the trials with a clearly defined primary outcome classed as the highest quality.