The importance of biological plausibility – we ignore it at our peril


Some forms of complementary and alternative medicine (CAM) are entirely plausible; that is to say, we understand the mechanism of action or, at the very least, we know that there could be a mechanism that is in accordance with known laws of nature. Herbalism is a good example; we know that plants contain pharmacologically active ingredients and, therefore, it is plausible that some herbs might generate pharmacological effects which, in turn, result in clinical benefit.

Other forms of CAM are entirely implausible. Some even fly in the face of our knowledge about nature, physiology or even common sense. For example, traditional acupuncturists are convinced that life-energy flows in meridians, and homeopaths believe that diluting a substance renders it not less but more potent.

Proponents of such treatments usually argue that it would be arrogant to assume that we already understand all nature’s secrets. They predict that as our knowledge grows, so does our understanding of the various concepts that underlie the treatment in question. In other words, proponents are convinced that the implausibility’s of today will become the plausibility’s of tomorrow.

This sounds alright, but is it really true? More often than not, we do not understand the mechanism of a complementary therapy, like homeopathy, or have insufficient knowledge to explain its assumptions. Frequently, we can be reasonably certain that there is no explanation that would be in line with the known laws of nature. In the case of homeopathy, we are reasonably certain that there cannot be a plausible explanation. Any clarification as to how ‘like cures like’ and how the absence of active molecules in homeopathic remedies can improve health would require re-writing of the laws of nature.

Nevertheless, there is a realistic chance that some forms of CAM, which must be currently classified as implausible, will turn out to be plausible. The chi and meridians of traditional acupuncturists, for instance, are implausible but acupuncture might still be effective via neurophysiological mechanisms that we are only beginning to understand.1In other areas of CAM (e.g. homeopathy or chiropractic as a treatment of non-spinal conditions), the likelihood of a plausible explanation is, however, close to zero.2,3

So, what is the relevance of all this? If we want to do efficient research, we should focus on those treatments that are already supported by biological plausibility. The danger of not adhering to this strategy is considerable; such as wasting time, money and experience on projects that have very little chance of success. This would not just be uneconomical but also unethical. Therefore, I am convinced that we ignore biological plausibility at our peril.

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