The Placebo Effect Revisited

This is a continuation of a very old post I did on the placebo effect. To summarise, a lot of people seem to think the placebo effect is somehow related to “mind over matter” and the body healing itself because it expects to be healed. In reality, the placebo effect is when an improvement is reported for any reason other than the physiological effects of a treatment. This does not automatically preclude any self-healing mechanisms but it means that the cause can be a lot more prosaic.

What I didn’t mention was the idea that there is no placebo effect. Or at least that it’s not an effect at all since the more objective your measure of patient condition the more the effect disappears (when compared to doing nothing at all). From the always excellent Science Based Medicine blog, I recommend this recent post by David Gorski which argues for this view using a recent trial on asthma.

I won’t make this wordy, the graphs from the study say more than words can. I present the two graphs in reverse order for effect. The study compared four interventions for asthma in people who have moderately severe asthma. This is a much more interesting setup for the study of the placebo effect than just treatment/placebo. The treatments were Albuterol (an asthma drug on the market, also commonly known as Ventolin), a placebo inhaler, the placebo treatment of sham acupuncture using a retractable needle. Below are the subjective results: what kinds of improvements did the patients feel?

Once that’s sunk in, behold the objective results: what measured lung capacity improvements were there?

Yes it’s true that even the “no treatment” group may have been experiencing an effect simply by participating in the study. Even so, this illustrates what is meant by the idea that placebo is not an actual effect. Or rather, there is an effect but it’s so small so as to be lost in the much greater effect(!) of doing nothing. And it does provide support against the idea that it’s an effect that can be harnessed, or that it’s ok to give placebos as part of a treatment program. At least for conditions with objective measures.

Unsurprisingly, the pro-placebo conclusion given in the study is to say black is white. To quote Gorski (emphasis mine), “the spin on this study is not that placeboes don’t result in objectively measurable improvements, which is the correct conclusion. Rather, the spin is that subjective symptoms are as important or more important than objective measures; so let’s use placeboes.”

Of course this is just one study and it may have some other flaws, although the protocol seems pretty basic and unequivocal. But the above reaction looks like an example of a well-established — and very sad — result in psychology. When people are presented with science that contradicts their belief, the most common response is to start believing science itself is bunk. If you’re feeling too optimistic today, this article by Chris Mooney on the science of why we don’t believe in science will fix that.

[EDIT]: After I wrote this up, Steve Novella did a post on Neurologica that I recommend, which discusses the same study — and presents the same 2 graphs in the same order.

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The thinly-veiled identity of lives and rants in Sydney. Views not his own, provided by hivemind. All my original work on this blog is licensed under a CC BY-NC License.

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