Elsevier

The Lancet

Volume 350, Issue 9081, 20 September 1997, Pages 834-843
The Lancet

Articles
Are the clinical effects of homoeopathy placebo effects? A meta-analysis of placebo-controlled trials

https://doi.org/10.1016/S0140-6736(97)02293-9Get rights and content

Summary

Background

Homoeopathy seems scientifically implausible, but has widespread use. We aimed to assess whether the clinical effect reported in randomised controlled trials of homoeopathic remedies is equivalent to that reported for placebo.

Methods

We sought studies from computerised bibliographies and contacts with researchers, institutions, manufacturers, individual collectors, homoeopathic conference proceedings, and books. We included all languages. Double-blind and/or randomised placebo-controlled trials of clinical conditions were considered. Our review of 186 trials identified 119 that met the inclusion criteria. 89 had adequate data for meta-analysis, and two sets of trial were used to assess reproducibility. Two reviewers assessed study quality with two scales and extracted data for information on clinical condition, homoeopathy type, dilution, “remedy”, population, and outcomes.

Findings

The combined odds ratio for the 89 studies entered into the main meta-analysis was 2·45 (95% CI 2·05, 2·93) in favour of homoeopathy. The odds ratio for the 26 good-quality studies was 1·66 (1·33, 2·08), and that corrected for publication bias was 1·78 (1·03, 3·10). Four studies on the effects of a single remedy on seasonal allergies had a pooled odds ratio for ocular symptoms at 4 weeks of 2·03 (1·51, 2·74). Five studies on postoperative ileus had a pooled mean effect-size-difference of −0·22 standard deviations (95% Cl −0·36, −0·09) for flatus, and −0·18 SDs (−0·33, −0·03) for stool (both p<0·05).

Interpretation

The results of our meta-analysis are not compatible with the hypothesis that the clinical effects of homoeopathy are completely due to placebo. However, we found insufficient evidence from these studies that homoeopathy is clearly efficacious for any single clinical condition. Further research on homoeopathy is warranted provided it is rigorous and systematic.

Introduction

Bh1tween 30 and 70% of patients in developed countries use complementary, alternatior unconventional medicine,1, 2, 3 even though high-quality scientific research on these practices is lacking.4 Homoeopathy is one of the most widespread and controversial of these therapies. There are two main theoretical tenets: the principle of “similars” and the use of dilutions called “potencies”.5 The principle of similars states that patients with particular signs and symptoms can be cured if given a drug that produces the same signs and symptoms in a healthy individual. The second principle is that remedies retain biological activity if they are repeatedly diluted and agitated or shaken between each dilution. These dilutions are said to produce effects even when diluted beyond Avogadro's number in which no original molecules of the starting substance remain. How the solution “remembers” information from the original substance is speculative.6

Mh1ny scientists think that homoeopathy violates natural laws7 and thus effect must be a placebo effect.8, 9 But use of and belief in the effectiveness of homoeopathy is widespread and growing among physicians and the public,10, 11, 12, 13 and advocates claim that there are measurable and reproducible effects over placebo.14 A systematic review of 107 controlled clinical trials in homoeopathy by Kleijnen et al in 1991 showed a surprising number of positive results, even among those that received high quality-ratings for randomisation, blinding, sample size, and other methodological criteria.15 Vote counts of positive and negative trials, as used in that review, can be misleading without a quantitative summary of results. Since that study was published, at least 50 more controlled trials in homoeopathy have been reported.

Wh1 aimed to assess whether the effect seen with homoeopathic remedies is equivalto that seen with placebo. If the hypothesis that all clinical effects of homoeopathy are due to placebo is correct, it would mean that in all properly conducted placebo-controlled trials on homoeopathy, one placebo had been compared with another. The overall results of these trials, in any disease, should vary randomly around a zero difference between groups. This placebo hypothesis would be falsified if all properly conducted comparisons of homoeopathy and placebo showed a pooled effect significantly different from zero difference, or if there is independently replicated evidence for an effect over placebo in at least one consistently applied homoeopathic approach. Of course, evidence of an effect over placebo would be stronger if both approaches showed “positive” effects and “non-believers” were involved in the trials. We have tested both of the above strategies (overall comparison and reproducibility comparisons) with quantitative meta-analytic methods.

Section snippets

Literature search and data sources

All published reports of controlled clinical trials of homoeopathy were collected with use of multiple sources: (1) the review by Kleijnen et al,15 which used an extensive search strategy for MEDLINE and EMBASE up to 1990; (2) a MEDLINE search by an information specialist from 1966 to August, 1995, with the full-text terms homeop* and homoeop*, and the MeSH terms homoeopathy, homoeopathy, and alternative medicine, and screening of all citations found; (3) contacts with homoeopathic researchers,

Literature search and study selection

186 trials were identified (excluding drug “provings”). Of these, one was a time-series, placebo-controlled single-case experiment, 14 involved assessment of physiological measures on healthy volunteers, and 38 did not include a placebo group, leaving 133 placebo-controlled trials evaluating treatment or prevention. Of these, three trials were not randomised, nine were unclear about randomisation and double-blinding, and in two trials a single-blind design was used but a statement on treatment

Discussion

The results of our meta-analysis are not compatible with the hypothesis that the clinical effects of homoeopathy are completely due to placebo. But there is insufficient evidence from these studies that any single type of homoeopathic treatment is clearly effective in any one clinical condition. The evidence in our overall analysis would be more compelling if there were independently replicated, large-scale rigorous trials of defined homoeopathic approaches in at least a few specific disorders.

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