In two years of writing about evidence-based medicine, I have largely managed to avoid the subject of homeopathy. It is the classic example of a medical practice developed before a scientific understanding of the basic mechanisms of health and disease existed. Unfortunately, it has remained true to 18th-century principles despite all the subsequent advances in medical knowledge. Controversial from its beginnings,1 homeopathy has long been employed by only a few health-care professionals, and surveys show only a tiny minority of citizens in most developed countries have used homeopathic treatment.2–4

It would seem safe, then, to dismiss and ignore this relic of prescientific medicine. However, homeopathy has managed to retain a small following in both human and veterinary medicine, and its proponents are sometimes visible and influential out of proportion to their numbers. Clients often ask me about using homeopathic remedies they have heard about from friends or online sources, often from veterinarians who support the practice.

What’s more, misleading information about homeopathy continues to be presented at major veterinary continuing education conferences and to appear in niche alternative veterinary medicine journals, which helps to create doubt about the scientific evidence concerning this practice. Attempts by regulators and professional organizations to discourage the use of homeopathy have had mixed results, thanks to vigorous lobbying against the scientific consensus by a vocal minority. Therefore, a brief evidence-based overview of veterinary homeopathy may still be useful to pet owners and veterinary professionals.

Basic principles

The first rule of homeopathy is that something which causes certain symptoms in a healthy person is the best treatment for those symptoms in someone who is sick. This is a principle that is known as the Law of Similars5 and clearly reflects a metaphorical approach to disease which, in modern medical science, has been replaced by specific pathophysiologic explanations derived from scientific research. Apart from this flaw, however, the Law of Similars has the obvious problem that if you give an ill patient something that creates symptoms of illness in normal individuals, you will often make them worse.

Samuel Hahnemann, the inventor of homeopathy, discovered this problem through trial and error with his own patients.5,6 Instead of recognizing his basic principle was flawed, however, he took the approach of greatly diluting his remedies, which reduced their ill effects. In the absence of the harm done by the traditional remedies used at the time, many of which were toxic to a certain degree, some of Hahnemann’s patients recovered after taking his diluted preparations. Since the only evidence available at the time for assessing efficacy was anecdote and subjective experience, this was interpreted as successful treatment.

This “success” led Hahnemann to develop the second principle of homeopathy—the Potentization by Dilution and Succussion. This is the idea that homeopathic medicines become more potent the less active ingredients they contain. (Succussion refers to shaking the remedies, since Hahnemann apparently also believed the agitation his medicines received as he traveled on horseback to see his patients somehow increased their curative power.5,6)

Finally, homeopathy relies on a complex process for individualizing the use of homeopathic preparations by evaluating the physical and mental experiences of patients and comparing them with experiences reported by healthy individuals testing specific homeopathic remedies. The details of this process are too involved to summarize here, but they involve a purely subjective and anecdotal process that has not been, and probably cannot be, validated through controlled scientific research.

The scientific evidence

Despite the inherent implausibility of these concepts and the general incompatibility of homeopathic theory with established principles of physiology, chemistry, pharmacology, and other modern disciplines in medical science, there has been a lot of preclinical and clinical research on homeopathic remedies and treatments. The majority of this has been published in journals devoted exclusively to homeopathy or other alternative therapies, and there is often a lack of proper methodological controls and significant risk of bias in these publications. Numerous systematic reviews of homeopathy in human medicine have been published, and the majority show no evidence of real or clinically meaningful effects beyond that of placebos.2,7-35 When sufficient studies are conducted and published by committed advocates for any practice, bias will inevitably lead to some apparently positive results, but such results have not been replicated or validated by consistent, unbiased investigation.

The veterinary literature concerning homeopathy is, as always, sparser than that in human medicine, but the same general assessment applies. Despite some ostensibly positive findings in low-quality studies with high residual bias risk, the preponderance of the evidence shows no real or replicable effects. Even dedicated proponents of homeopathy are unable to find convincing high-quality research evidence for the practice when they apply accepted methods for evaluating the literature.36–42

Evidence-based medicine is always about a flexible and probabilistic understanding, and absolute, immutable conclusions are anathema to the core principles of this approach. However, evaluating homeopathy at every level—from biologic plausibility to preclinical and in vitro research to clinical trials—leads to as confident a conclusion as science can ever muster: the practice has no benefits.

The future of veterinary homeopathy

Given this scientific conclusion, it seems clear homeopathy can have no legitimate role in modern veterinary medicine. It is unethical to offer clients ineffective remedies, and even when the treatments themselves may do no harm, they can mislead clients and discourage the use of truly effective treatments.

A number of regulators and professional organizations have recognized this and taken action. The Federal Trade Commission (FTC) and the U.S. Food and Drug Administration (FDA) have recently issued statements warning the public that claims for the safety and efficacy of homeopathy are not supported by science. In the veterinary field, the Australian Veterinary Association (AVA), British Veterinary Association (BVA), and the Royal College of Veterinary Surgeons (RCVS) all have clear policy statements acknowledging homeopathy as ineffective and discouraging its use. Numerous specialty colleges in the U.S. and abroad have issued similar statements. The American Veterinary Medical Association (AVMA), unfortunately, declined to adopt a similar policy in 2014 despite a finding from its own council on research that, “there is no clinical evidence to support the use of homeopathic remedies for treatment or prevention of diseases in domestic animals.”43

Political and economic considerations, as well as vehement advocacy and misleading information from proponents of homeopathy, have kept the method alive despite the clear scientific evidence against it. Hopefully, the current trend toward accepting the verdict of science will remain, and homeopathy will continue to decline and eventually disappear from veterinary journals and continuing education. Undoubtedly, some practitioners and clients will always choose anecdote and wishful thinking over evidence. However, as members of a scientific medical professional, we have a responsibility to provide effective care to our patients and honest, accurate information to our clients. Meeting this core ethical responsibility leaves no place for equivocation or failing to clearly discourage the use of homeopathy.

Brennen McKenzie, MA, MSc, VMD, cVMA, discovered evidence-based veterinary medicine after attending the University of Pennsylvania School of Veterinary Medicine and working as a small animal general practice veterinarian. He has served as president of the Evidence-Based Veterinary Medicine Association and reaches out to the public through his SkeptVet blog, the Science-Based Medicine blog, and more. He is certified in medical acupuncture for veterinarians. Columnists’ opinions do not necessarily reflect those of Veterinary Practice News.

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