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Is the placebo effect real? A closer look at the PLoS study on the benefits of placebo in treating Irritable Bowel Syndrome (IBS).

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If only placebo effects were real …

The journal PLoS published a randomized, controlled study reporting the benefits of placebo in the treatment of Irritable Bowel Syndrome (IBS).  The study, based on the idea that the body has a “powerful self-healing network,” has been purported to demonstrate that placebos actually do something beneficial for patients’ diseases and are “profoundly good news to anyone but investors in Pfizer, Roche and GlaxoSmithKline”.

I wouldn’t rush to sell my shares in drug companies (full disclosure: I don’t have any such shares, except perhaps within mutual funds) or give up on the benefit of FDA-approved medications.  The PLoS study compared two groups:

  • Patients who were told they were being given a placebo (and were told that the placebo effect is powerful, the body can automatically respond to taking placebo pills like Pavlov’s dogs who salivated when they heard a bell, a positive attitude helps but is not necessary, and taking the pills faithfully is critical), and
  • Patients who were told they were being given no treatment.

The study assessed the patients’ report of how they were doing. There was no objective measure included to test whether there was any change in inflammation or any other real change in the body from the treatment.

The study did find a difference in what patients reported.  The study found a statistically significant  global improvement in the group given placebo compared to the group getting no treatment.  That sounds good, but global improvement was measured on a 1 to 7 scale.  On average, the no treatment group reported no change, while the placebo group reported just slight improvement, not moderate or substantial improvement.  As is done all too often, the graph of the results that was published in the PLoS study lopped off large portions of the scale in what seems to me to be an attempt to make the global improvement results look more significant than they really were.

These two graphs show the same data. The graph on the left shows how the data was presented in the study, magnifying the apparent improvement associated with placebo, while the graph on the right provides a more accurate illustration of the degree of benefit found.

The PLoS study does show that patients who are told they are being given a placebo report slight improvement in their condition, but the placebo may only be changing how the patients respond to a survey, not any actual change in their condition.  The PLoS study did not look for, much less demonstrate, any benefit in any objectively measurable sign of actual healing.

I’m quite enthusiastic about some of the modern miracle drugs we have.  They’ve been rigorously tested and proven to help correct physiologic changes associated with a wide range of diseases.  I specialize in the treatment of psoriasis.  New miracle drugs like etanercept, infliximab and adalimumab are extraordingary treatments for patients with severe psoriasis.  In the study of those drugs, placebo groups had improvements in their psoriasis of about 15 to 20 percent.  But that improvement appears to be largely due to the way the study was done, not to actual improvements in the disease.

Placebo effects may be great in theory, but they appear ephemeral, disappearing when subjected to close scrutiny.

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