What is the placebo effect?

Some of you will have seen some correspondence on this blog about placebos and the placebo effect. I think some further discussion is necessary.

Placebo is a latin word for “I shall please”.

A placebo is a sham or simulated medical intervention. Sometimes patients given a placebo treatment will have a perceived or actual improvement in a medical condition, this phenomenon is called the placebo effect.


In medical research, placebos are given as control treatments. Studies depend on the use of placebos to measure the treatment effect of an active comparator. Common placebos are inert tablets, sham surgery and other procedures. 


Placebos can have a surprisingly positive effect on a patient who knows that the given treatment may or may not be an active drug, as compared with a control group who knowingly did not get a placebo. There is scientific evidence that this placebo effect is a real effect and the body responds differently to those who do not receive a placebo. For example, different areas of the brain are activated as a result of the placebo-effect compared to those not receiving a placebo. 

Placebos are widely used in medical research and medicine; in fact, it is part of the response to any active medical intervention. The placebo effect points to the importance of perception and the brain’s role in physical health. 


However, when used as treatment in clinical medicine (as opposed to laboratory research), the deception involved in the use of placebos creates tension between the Hippocratic Oath and the honesty of the doctor-patient relationship. The United Kingdom Parliamentary Committee on Science and Technology has stated that: “…prescribing placebos… usually relies on some degree of patient deception” and “prescribing pure placebos is bad medicine. Their effect is unreliable and unpredictable and cannot form the sole basis of any treatment on the NHS.” [UK Parliamentary Committee Science and Technology Committee. “Evidence Check 2: Homeopathy”]

In summary it is therefore unethical to give someone a placebo, or something that is known not to work and relies on the placebo effect, in routine clinical practice. The use of placebos in clinical trials is different; study subjects are fully informed of the possibility that they may be given a placebo and they have to sign a consent form. 

“Therefore if someone responds to a treatment or intervention it does not necessarily mean that the treatment or intervention works. The response could be due to the placebo effect. The only way to assess whether or not the treatment actually works is to do a blind or double-blind comparison, in which the intervention is compared to a placebo or shame procedure. This process controls for the placebo effect.”

“I would recommend reading “Bad Science” by Ben Goldacre, who goes into the placebo effect in some detail and how it has been used in the past to promote ineffective treatments. It is a very interesting read.”

Additional reading: placebo, Bad Science

Other relevant posts on this blog


CCSVI – Bad Science
22 Apr 2011
If any one is interested in CCSVI they should read “Bad Science” by Ben Goldacre; the book provides the social context to the CCSVI phenomenon. Please see badscience.net.

6 thoughts on “What is the placebo effect?”

  1. Prof G, did you too have to swear by Apollo, the healer, Asclepius, Hygieia, and Panacea when taking your Hippocratic Oath?The Hippocratic Oath is outdated. In an era where assisted suicide is likely to be introduced into British law within the coming years, such an oath will need to be revised.

  2. I was a bit disappointed in 'Bad Science' – talk about labouring a point (somewhat repetitive), and of course, he is generally preaching to the converted anyway! I concede that there were some interesting points, but I also thought that the author didn't credit his fellow humans with much intelligence.

  3. Re "Therefore if someone responds to a treatment or intervention it does not necessarily mean that the treatment or intervention works"Placebo and skepticism are not without limits. Could lead to blindness. It's all about how you define "responds", namely to what extend you comprehend the patient's status before and after the treatment.

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