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Placebo Effect


Explanations > Theories > Placebo Effect

Description | Example | So What? | See also | References 



The 'placebo effect' occurs where ineffective medical interventions have actual effect. For example where a doctor gives a patient a non-pharmaceutical pill, yet the patient responds as if it was pharmaceutically effective.

The placebo effect for pills increases with:

  • Larger pills
  • More pills
  • Red or orange ('hot') pills
  • The brand of the pill
  • More expensive pills

The reason the placebo works is because the patient believes it will be effective. There may also be some conditioning effect. The credibility of the person administering the placebo is hence another important factor, as is the manner of administration.

People who are higher in ego resilience and agreeableness, and with lower angry neuroticism, tend to be more susceptible to placebos, which are reflected in their more easily forming bonds with prescribing doctors. These people also tend to have more opioid receptor activity in the brain.

Alternative medicines, from acupuncture to homeopathy have been considered as working primarily (or completely) due to the placebo effect. 'Quack medicines' peddled by charlatans depend for their success on the placebo effect.

Doctors know that this often works, which is why they use it when there is no clear alternative. There is an ethical dilemma with using a placebo, as it necessarily involves deception.

The placebo is by no means a cure-all and there are many diseases where it has no effect. The effect also varies with the individual, their credulity and how convinced other people they meet are that it will work.

More generally, the 'placebo effect' is also used to describe any situation where suggestion is used to some effect or where the principle of 'mind over body' is significant.

'Placebo' is Latin for 'I shall please'.

The 'nocebo effect' (Latin for 'I will harm') is a reverse of the placebo, where interventions have a negative effect.


A person complains of regular headaches and normal analgesics do not seem to have an effect. A doctor prescribes a placebo but says it is a new wonder-drug. The headaches magically disappear.

So What?

Using it

Make suggestions that people will be able to do something or something will happen to them because of some intervention you have used.


If you are unsure that people have good intent for you, beware of them making linked suggestions. It it still always a good idea to believe doctors.

See also

Belief Bias, Belief Perseverance, Classical Conditioning, Source Credibility


Beecher, H.K.  (1955). The Powerful Placebo, Journal of the American Medical Association, 159, 17

Kennedy, W P. (1961). The Nocebo Reaction. Medical World, 95, 203-205

Peciņa, M., Azhar, H., Love, T., Lu, T., Fredrickson, B., Stohler, C., and Zubieta, J. (2012). Personality Trait Predictors of Placebo Analgesia and Neurobiological Correlates, Neuropsychopharmacology 


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