Homeopathy is a form of alternative medicine based on the concept that increasing dilution of a substance leads to a stronger treatment effect.
The authors of the new paper, published in BMJ Evidence-Based Medicine, also found that a quarter of the 90 randomized published trials on homeopathic remedies they analyzed changed their results before publication.
The benefits of homeopathy touted in studies may be greatly exaggerated, suggest the authors, Gerald Gartlehner, MD, of Danube University, Krems, Austria, and colleagues.
The results raise awareness that published homeopathy trials represent a limited proportion of research, skewed toward favorable results, they wrote.
“This likely affects the validity of the body of evidence of homeopathic literature and may substantially overestimate the true treatment effect of homeopathic remedies,” they concluded.
Homeopathy as practiced today was developed approximately 200 years ago in Germany, and despite ongoing debate about its effectiveness, it remains a popular alternative to conventional medicine in many developed countries, the authors noted.
According to the National Institutes of Health, homeopathy is based on the idea of “like cures like,” meaning that a disease can be cured with a substance that produces similar symptoms in healthy people, and the “law of minimum dose,” meaning that a lower dose of medication will be more effective. “Many homeopathic products are so diluted that no molecules of the original substance remain,” according to the NIH.
Homeopathy is not subject to most regulatory requirements, so assessment of effectiveness of homeopathic remedies is limited to published data, the researchers said. “When no information is publicly available about the majority of homeopathic trials, sound conclusions about the efficacy and the risks of using homeopathic medicinal products for treating health conditions are impossible,” they wrote.
Study methods and findings
The researchers examined 17 trial registries for studies involving homeopathic remedies conducted since 2002.
The registries included clinicaltrials.gov, the EU Clinical Trials Register, and the International Clinical Trials Registry Platform up to April 2019 to identify registered homeopathy trials.
To determine whether registered trials were published and to identify trials that were published but unregistered, the researchers examined PubMed, the Allied and Complementary Medicine Database, Embase, and Google Scholar up to April 2021.
They found that approximately 38% of registered trials of homeopathy were never published, and 53% of the published randomized, controlled trials (RCTs) were not registered. Notably, 25% of the trials that were registered and published showed primary outcomes that were changed compared with the registry.
The number of registered homeopathy trials increased significantly over the past 5 years, but approximately one-third (30%) of trials published during the last 5 years were not registered, they said. In a meta-analysis, unregistered RCTs showed significantly greater treatment effects than registered RCTs, with standardized mean differences of –0.53 and –0.14, respectively.
The study findings were limited by several factors including the potential for missed records of studies not covered by the registries searched. Other limitations include the analysis of pooled data from homeopathic treatments that may not generalize to personalized homeopathy, and the exclusion of trials labeled as terminated or suspended.