Veterinary homeopathy: meta-analysis of randomised placebo-controlled trials

•We report a systematic review and meta-analysis of randomised controlled trials (RCTs).•We tested the hypothesis that the outcome of veterinary homeopathic intervention is distinguishable from that of placebos.•For 15 eligible RCTs with extractable data, pooled odds ratio (OR) = 1.69 [95% confidence interval (CI), 1.12 to 2.56]; P = 0.01.•Nine of the 15 RCTs displayed high risk of bias; only two comprised reliable evidence.•For the two RCTs with reliable evidence, OR = 2.62 [95% CI, 1.13 to 6.05]; P = 0.02).•There is some very limited evidence that homeopathic intervention in animals is distinguishable from that of placebos.•The deficient quality of the evidence hinders a more decisive conclusion.

BackgroundMeta-analysis of randomised controlled trials (RCTs) of veterinary homeopathy has not previously been undertaken. For all medical conditions and species collectively, we tested the hypothesis that the outcome of homeopathic intervention (treatment and/or prophylaxis, individualised and/or non-individualised) is distinguishable from corresponding intervention using placebos.MethodsAll facets of the review, including literature search strategy, study eligibility, data extraction and assessment of risk of bias, were described in an earlier paper. A trial was judged to comprise reliable evidence if its risk of bias was low or was unclear in specific domains of assessment. Effect size was reported as odds ratio (OR). A trial was judged free of vested interest if it was not funded by a homeopathic pharmacy. Meta-analysis was conducted using the random-effects model, with hypothesis-driven sensitivity analysis based on risk of bias.ResultsNine of 15 trials with extractable data displayed high risk of bias; low or unclear risk of bias was attributed to each of the remaining six trials, only two of which comprised reliable evidence without overt vested interest. For all N = 15 trials, pooled OR = 1.69 [95% confidence interval (CI), 1.12 to 2.56]; P = 0.01. For the N = 2 trials with suitably reliable evidence, pooled OR = 2.62 [95% CI, 1.13 to 6.05]; P = 0.02).ConclusionsMeta-analysis provides some very limited evidence that clinical intervention in animals using homeopathic medicines is distinguishable from corresponding intervention using placebos. The low number and quality of the trials hinders a more decisive conclusion.