Placebo Effects Revisited

In the Wall Street Journal last week was a particularly bad article by Melinda Beck about acupuncture. While there was token skepticism (by Edzard Ernst, of course, who is the media’s go-to expert for CAM), the article credulously reported the marketing hype of acupuncture proponents.

Toward the end of the article Beck admits that “some critics” claim that acupuncture provides nothing more than a placebo effect, but this was followed by the usual canard:

“I don’t see any disconnect between how acupuncture works and how a placebo works,” says radiologist Vitaly Napadow at the Martinos center. “The body knows how to heal itself. That’s what a placebo does, too.”

That is a bold claim, and very common among CAM proponents, especially acupuncturists. As the data increasingly shows that acupuncture (and other implausible treatments) provides no benefit beyond placebo, we hear the special pleading that placebos work also.

But is that true? It turns out there is a literature on the placebo effect itself, and the evidence suggests that placebos generally do not work.

That may seem counter-intuitive, since the gold standard of clinical trials is placebo-controlled, because placebo effects can be quite large. However, most such trials do not contain a no-treatment arm (comparing a placebo intervention to nothing at all). What this means, as I have written about before, is that placebo effects, as measured in clinical trials, includes a host of factors – everything other than a physiological response to an active treatment.

These placebo effects include the bias of the researchers, the desire of the subjects to please the researchers and to get well, non-specific effects of receiving medical intervention and attention, and other artifacts of the research process. When we remove all of these biases and artifacts, is there a real effect left behind – what most people think of when they think of “the” placebo effect: a mind-over-matter but real improvement?

Proponents of so-called CAM would like you to believe that “the” placebo effect is all a real biological effect resulting from the body’s self-healing ability. But it turns out, this is simply not true.

Hróbjartsson  and Gøtzsche have been studying the placebo effect for years, reviewing the literature, especially for trials that contain a no-treatment arm. Their most recent review is very illuminating. They conclude:

We did not find that placebo interventions have important clinical effects in general. However, in certain settings placebo interventions can influence patient-reported outcomes, especially pain and nausea, though it is difficult to distinguish patient-reported effects of placebo from biased reporting. The effect on pain varied, even among trials with low risk of bias, from negligible to clinically important. Variations in the effect of placebo were partly explained by variations in how trials were conducted and how patients were informed.

Let’s break this down a bit. First, they found that when you look at any objective or clinically important outcome – the kinds of things that would indicate a real biological effect – there is no discernible placebo effect. There is no mind-over-matter self healing that can be attributed to the placebo effect.

What the authors found is also most compatible with the hypothesis that placebo effects, as measured in clinical trials, are mostly due to bias. Specifically, significant placebo effects were found only for subjectively reported symptoms. Further, the size of this effect varied widely among trials.

This latter feature is very important. If there were a significant physiological placebo effect we would expect to see a consistent or baseline effect among trials. The tremendous variability suggests that it was the rigor of trial design that allowed for lesser or greater bias resulting in a measured placebo effect.


Meta-regression analyses showed that larger effects of placebo interventions were associated with physical placebo interventions (e.g. sham acupuncture), patient-involved outcomes (patient-reported outcomes and observer-reported outcomes involving patient cooperation), small trials, and trials with the explicit purpose of studying placebo.

So the more patients were involved in the reporting of outcomes (as opposed to measuring outcomes) the greater the placebo effect. This is most consistent with bias as a cause. Also, as has been reported before, physical interventions result in a large placebo effect.

Some have hypothesized that time and attention provided by some “alternative” practitioners result in a greater placebo effect, justifying the intervention. However, that was not a factor apparent in this study. Another study, comparing placebo effect sizes for homeopathic treatments and mainstream treatments (which are comparable in terms of the physical intervention) found no difference in placebo effect sizes.


Existing evidence strongly suggests that placebo effects are mostly comprised of bias in reporting and observation and non-specific effects. There is no measurable physiological benefit from placebo interventions for any objective outcome. There is a measured benefit for some subjective outcomes (mostly pain, nausea, asthma, and phobias), but the wide variation in effect size suggests this is due to trial design (and therefore bias) rather than a real effect.

In any case, any perceived benefit in subjective symptoms seems to be greater for physical interventions (perhaps a hands-on benefit) but is the same for mainstream vs novel treatments.

Therefore, there is no justification to be found in the placebo effect for using unscientific or dubious interventions. Placebo medicine is a sham. And any potential placebo benefit worth having can be fully realized with science-based interventions.

Which means that Dr. Napadow may have been unwittingly correct when he said that acupuncture is no different from placebo.

Posted in: Acupuncture, Homeopathy, Science and Medicine

Leave a Comment (32) ↓