The fundamental concept of science-based medicine (SBM) is that medical practice should be based upon the best available science. This may seem obvious, but there are many important details to its application, such as the relationship between clinical and basic science. Clinical claims require clinical evidence, but clinical evidence can be tricky and is often preliminary. It is therefore helpful (I would say essential) to view the clinical evidence in light of all of the rest of science.

A thorough basic and clinical science analysis of a medical claim can be summarized by the term “plausibility,” or “prior probability” if you want to put it into statistical terms. When we say a certain belief is plausible we mean it is consistent with what we know from the rest of science. In other words, because of the many weaknesses of clinical evidence, in order for a therapy to be generally accepted as part of SBM it should have a certain minimal supporting clinical evidence and overall scientific plausibility.

These can exist in different proportions – for example one therapy may be highly plausible (it would be shocking if it were not true) and have modest supporting clinical evidence, while another may have unknown plausibility but with solid clinical evidence of efficacy. But no therapy should have clinical evidence that suggests lack of efficacy, nor extreme implausibility (not just an unknown mechanism, but no possible mechanism).

The poster child for extreme scientific implausibility within medicine is, arguable, homeopathy. Its “law of similars” is little more than sympathetic magic, and its “law of infinitessimals” leads to concoctions diluted to the point that they have zero active ingredient and only the magical memory left behind. It is this reality which inspired a recent review to characterize homeopathy as “witchcraft.”

What about the clinical evidence? The clinical evidence, when taken as a whole, and even if we set aside the question of plausibility, shows that homeopathy does not work. Decades of research have failed to provide supporting evidence for any application of homeopathy. It has failed to reject the null hypothesis, to show efficacy, to allow for the recommendation of homeopathy for any indication, to differentiate homeopathy from a placebo – in other words, homeopathy does not work.

If we consider the SBM criteria above, we can summarize homeopathy by saying it has extreme implausibility and the clinical evidence shows lack of efficacy. It should not work, and it does not work. There is no legitimate controversy about this. The only think keeping homeopathy alive are delusional proponents and a public (including many regulators) who do not know what homeopathy truly is.

Proponents, however, are desperately trying to keep their pseudoscience alive by misrepresenting the evidence and the arguments of homeopathy critics. A recent example of this is a paper by Peter Fisher, the Clinical Director Royal London Hospital for Integrated Medicine, and a prominent homeopath. He is trying to coin the phrase “negative plausibility bias.” His argument, essentially, is that the evidence shows homeopathy works (at least as well as medical treatments that do not work, which is an odd argument), but there is a negative plausibility bias against homeopathy which motivates scientists to reject this evidence. Fisher is both wrong and irrelevant in this position.

Fisher is wrong in arguing that the clinical evidence supports the efficacy of homeopathy. He does this by cherry picking positive studies (which are part of the noise of any clinical research), a common strategy. Meanwhile, systematic reviews do not show supporting evidence for homeopathy. Worse for homeopathy, there is a clear pattern in the research. The better designed and controlled the study, the more negative the results – a clear pattern of lack of efficacy. Even reviews that desperately try to spin the results in a positive way in the end show there is no evidence to support the efficacy of homeopathy.

The main point of the article, however, is to dismiss the scientific assessment of homeopathy as a “bias.” It seems like it is news to Fisher that plausibility is not a bias – it’s science.

Interestingly, Fisher claims that the law of similars part of homeopathy is not even controversial – and then he makes the same, tired analogies to hormesis and paradoxical drug effects, which actually have no relevance to homeopathy. Homeopathy “ingredients” are chosen for magical reasons that have no relationship to actual biology or chemistry. Further, the high dilutions of homeopathic preparations render such analogies invalid. Fisher and other homeopaths are just fishing for any possible hand-waving justification for homeopathy, but they lend nothing to its plausibility because they fail to make a scientifically coherent argument.

Fisher then essentially argues that the clinical evidence shows homeopathy works (wrong) but is rejected because of the “negative plausibility bias.” There is a kernel of truth to his view in that, in the face of extreme scientific implausibility, even modestly positive clinical evidence is looked upon as insufficient and not definitive. We can look at it this way – what are the odds that a mountain of solid basic science is wrong vs some sloppy and tricky clinical research is wrong? It would take overwhelmingly rigorous and positive clinical evidence to call into question long established principles of basic science. Homeopathy does not come anywhere close – even if we take the distorted and incorrect view of the clinical evidence Fisher is pushing.

The article is essentially Fisher whining that the scientific community is not ignoring the extreme scientific implausibility of homeopathy.

Fisher also tries to make a tu quoque argument – recycling yet another old ploy of medical pseudoscientists. He says that the evidence for antibiotic use in upper respiratory tract infections (URTI) is no different than homeopathy but practitioners use antibiotics and not homeopathy. The evidence base for any other practice is irrelevant to homeopathy, but even that aside his argument is a curious one. I agree that systematic reviews fail to show efficacy for routine antibiotic use in URTI. Therefore – they should not be used. In fact there are efforts within mainstream medicine to reduce the use of antibiotics in URTI, and to eliminate their routine use.

The story with URTI is more complex, however, because some people do get bacterial interference with URTI and there may be a role for antibiotics in selected cases – the trick is in knowing how to select those cases. More research is legitimately needed to explore these issues.

The only consistent position, therefore, is to favor the elimination of routine antibiotic use in URTI, based upon current evidence, and also to favor the complete elimination of homeopathy as a practice. Meanwhile, it is reasonable to do more research into a possible limited role of antibiotics in selected cases (based partly on plausibility). It is also reasonable to favor the abandonment of any further research into homeopathy, based on its extreme scientific implausibility.

You can call it a “negative plausibility bias” or you can call it science, based upon your perspective.


Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.