Adverse effects of homeopathy, what do we know? A systematic review and meta-analysis of randomized controlled trials

Objectives: Homeopathy is a popular treatment modality among patient, however there is sparse research about adverse effects of homeopathy. A concept unique for homeopathy, is homeopathic aggravation that is understood as a transient worsening of the patients' symptoms before an expected improvement occurs. From a risk perspective it is vital that a distinction between homeopathic aggravations and adverse effects is established. There is a lack of systematic information on how frequent adverse effects and homeopathic aggravations are reported in studies. Therefore, a systematic review and meta-analysis were performed. Design and setting: Sixteen electronic databases were searched for Randomized Controlled Trials (RCTs). The searches were limited from the year 1995 to January 2011. Forty-one RCTs, with a total of 6.055 participants were included. A subtotal of 39 studies was included in the additional meta-analysis. Results: A total of 28 trials (68%) reported adverse effects and five trials (12%) reported homeopathic aggravations. The meta-analysis (including six subgroup comparisons) demonstrated that no significant difference was found between homeopathy and control with OR 0.99, 95% CI 0.86-1.14, I-2 = 54%. More than two third of the adverse effects were classified as grade 1(68%) and two third were classified as grade 2 (25%) and grade 3 (6%) according to the Common Terminology Criteria for Adverse Effects. Homeopathic aggravation was classified as grade 1 (98%) and grade 3 (2%), suggesting that homeopathic aggravations were reported to be less severe than adverse effects. The methodological quality according to a method recommended in the Cochrane handbook for RCTs, was high. Conclusion: Adverse effects including the concept of homeopathic aggravations are commonly reported in trials. The meta-analysis demonstrated that the proportion of patients experiencing adverse effects to be similar for patients randomized to homeopathic treatment compared to patients randomized to placebo and conventional medicine. (C) 2016 Elsevier Ltd. All rights reserved.