Placebos appear to work even when individuals know they’re placebos

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Placebos are essentially inactive agents that are typically usually used in trials used to determine if a drug has genuine benefits or not. In most so-called ‘randomised, controlled trials’ individuals are assigned to take the medication or treatment being tested, while the rest get a placebo. If it turns out that the group receiving the active treatment experience benefits that are statistically significantly greater than those experienced by the placebo-taking group, then this would be evidence that the drug was more effective than placebo.

The reason for testing drugs and other treatments in this way is because of the placebo response – the improvement individuals may experience which can be related to all sorts of things including the way a practitioner talks to them, how well heard and honoured they feel, how much time they have with a practitioner, and expectations regarding their condition, its treatment and prognosis (likely outcome).

Usually, randomised controlled trials are ‘double-blind’ in nature, which means neither the researchers nor the study participants know whether an individual patient is getting the active treatment or placebo. In other words, individuals taking a placebo will usually not know that, and will believe that they have (usually) a 50:50 chance of being on the active treatment. In randomised controlled trials, an individual’s belief that they might be on the active treatment might contribute considerably to the placebo response. In theory, if an individual knew they were on placebo only, we wouldn’t expect much of a placebo response.

This concept was tested in a study which was published recently in the on-line journal PLoS ONE. In this study, individuals with irritable bowel syndrome were treated with a placebo, and told that’s exactly what they were taking. The bottle holding the placebos they were given even had the word ‘placebo’ written on them. Another group of patients with IBS were given no treatment for comparison.

After 3 weeks, 39 per cent of the group receiving nothing reported an improvement in their symptoms. In the placebo group, this figure was 59 per cent. This difference was statistically significant. The authors describe the effect as “clinically meaningful”.

Almost 3 years ago one of my blogs looked at the ethics of prescribing placebos in practice. Apparently, about half of doctors in the US do this, but are generally not transparent about it. Another approach, as I mentioned in that blog post, would be for doctors to prescribe a placebo, but also explain to their patients exactly what they’re doing. I suggested that this might jeopardise the value of the placebo.

However, this latest research suggests that perhaps I needn’t worry: it appears that individuals can get genuine benefit from a placebo, even when they know that what it is.


1. Kaptchuk TJ, et al. Placebos without Deception: A Randomized Controlled Trial in Irritable Bowel Syndrome. PLoS ONE 5(12): e15591.

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