ArticlesAre the clinical effects of homoeopathy placebo effects? Comparative study of placebo-controlled trials of homoeopathy and allopathy
Introduction
Homoeopathy is a widely used but controversial complementary or alternative therapy.1, 2, 3 The basic premise is that like is cured by like (similia similibus curentur)—diseases can be treated by substances that produce the same signs and symptoms in a healthy individual.4, 5 The preparation of remedies involves serial dilution, commonly to the extent that no molecules of the original substance remain, and vigorous shaking between dilutions (potentisation). During this process information is thought to be transferred from the diluted substance to the solvent,6 which in the light of current knowledge seems implausible. Many people therefore assume that any effects of homoeopathy must be non-specific placebo effects.7
Bias in the conduct and reporting of trials is a possible explanation for positive findings of placebo-controlled trials of both homoeopathy and allopathy (conventional medicine).8, 9 Publication bias is defined as the preferential and more rapid publication of trials with statistically significant and beneficial results than of trials without significant results.10 The low methodological quality of many trials is another important source of bias.11 These biases are more likely to affect small than large studies; the smaller a study, the larger the treatment effect necessary for the results to be statistically significant, whereas large studies are more likely to be of high methodological quality and published even if their results are negative. We examined the effects of homoeopathy and conventional medicine observed in matched pairs of placebo-controlled trials, assessed trial quality and the probability of publication and related biases, and estimated results of large trials least affected by such biases.
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Literature search and data sources
We updated a previous comprehensive search for placebo-controlled trials of homoeopathy, which covered publications up to August, 1995.12 We searched 19 electronic databases, including specialised homoeopathic and complementary-medicine registries, covering the period from 1995 to January, 2003: MEDLINE, Pre-MEDLINE, EMBASE, DARE, CCTR, CDSR, CINAHL, AMED, MANTIS, Toxline, PASCAL, BIOL, Science Citation Index, CISCOM, British Homeopathic Library, the Homeopathy Abstract page, HomInform
Results
We identified 165 potentially eligible reports of placebo-controlled trials of homoeopathy and excluded 60 reports. The commonest reasons for exclusion were insufficient information (precluding the calculation of odds ratios), ineligible study design, multiple publication, and inability to identify a matching trial of conventional medicine (figure 1). We included 105 publications that reported on a total of 110 independent trials of homoeopathy (webappendix 1) and 110 publications of 110
Discussion
We compared the effects of homoeopathy and conventional medicine that are seen in placebo-controlled trials, examined the presence of bias resulting from inadequate methods and selective publication, and estimated results in trials least affected by these biases. We assumed that the effects observed in placebo-controlled trials of homoeopathy could be explained by a combination of methodological deficiencies and biased reporting. Conversely, we postulated that the same biases could not explain
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