Nov 08 2007
In a recent Slate article, Darshak Sanghavi exposes the mythology surrounding the placebo. He correctly points out that the common belief that the “placebo effect” is primarily a mind-over-matter real physical healing is nothing more than a myth. Reviews of the medical literature show that for subjective symptoms, especially pain, there is a decrease in the the reporting of such symptoms by about 30% with placebo, or inactive, treatment. However, for biological or objective outcomes, like survival from cancer, there is no significant or measurable placebo effect – sugar pills do not increase your chance of surviving cancer.
Rather than a placebo effect, there is, rather, a trial effect – namely the fact that a patient is enrolled in a clinical trial will improve their outcome. This is due to a host of factors – being in a trial means getting more medical care and attention, and it inspires patients to think more about their care and thereby to take better care of themselves, for example by being more compliant with their treatments. In those trials where a placebo group was further compared to a group without a real treatment or placebo treatment – an observation group – there is no difference in outcome between placebo and observation groups. So getting the placebo had no advantage – the belief that one was being treated was not enough to cause a real biological healing.
Why, then, Sanghavi asks, are we so insistent on placebo-controlled trials? While I agree with Sanghavi that we need to listen to the evidence, and be clear that there is no biological response to placebo treatments, I think he goes too far in recommending that placebo-controlled groups are not necessary. The real reason for a placebo is not to rule out a real biological effect from the belief of being treated, but to assure proper blinding of those who are assessing the outcomes (which may include the subject themselves, the treating physician, or a third observer not otherwise involved in the trial).
Proper blinding is necessary to eliminate bias in assessing the outcomes of the trial. Bias is a huge problem in clinical trials. The overall pattern of research is that the less well controlled a trial the more it will reflect the biases of the researchers. The best blinded and controlled trials tend to be the most reliable (in terms of predicting future trends in the research literature).
In addition, scientific medicine is being infiltrated by ideologically driven beliefs and practitioners. Under the umbrella of so-called alternative medicine, there is a host of dubious and unscientific treatments, all clamoring for scientific respectability, with true-believer advocates doing the research. We need to move toward more rigorous trials designs and higher standards of blinding – not weaker. Sanghavi is living in a world of scientific researchers testing plausible treatments under reasonable conditions. But we need a system that can deal with the nonsense as well, otherwise they will exploit the weaknesses in the system to further infiltrate medicine.
Also, I am not letting the pharmaceutical and supplement industry off the hook – review of literature shows that industry sponsored research is more likely to support the desires of industry. Again – bias has an effect, and the only way to weed it out is through methodological rigor, including blinding of trials.
So while I agree with Sanghavi that we need to dispel the placebo myth, and I also agree with him that in some cases (like doing sham surgery as a placebo) we can control trials in other ways, for the most part we still need placebo-controlled trial designs to maximize blinding and thereby minimize bias in clinical trials.
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