Placebo Effect


The placebo effect is the beneficial therapeutic effect of an inactive or nonspecific treatment. The placebo effect may explain the benefit of complementary medicine such as aromatherapy and reflexology.

Keywords: placebo; nocebo; complementary medicine; clinical trials; ethics

Figure 1.

Components of a medicine. The effects of an active medicine in a clinical trial are made up of three components: pharmacological effect, true placebo effect and nonspecific effects. The perceived placebo effect is the total effect of placebo treatment and this includes two components: the true placebo effect related to belief in the efficacy of the treatment and nonspecific effects due to natural recovery. In order to determine the magnitude of any ‘true’ placebo effect it is necessary to compare the effects of the placebo control medicine with those of a no‐treatment control group.

Figure 2.

Changes in cough frequency after treatment with a placebo medicine (open symbols) and a cough medicine in capsule form (30 mg dextromethorphan) in patients with cough associated with common cold. Reprinted with permission from Journal of Pharmacy and Pharmacology (2002) 52: 1139.

Figure 3.

Pain relief obtained by branded aspirin compared with unbranded aspirin for relief of headache pain. Based on data by Branthwaite and Cooper .



Benson H (1996) Timeless Healing. London: Simon & Schuster.

Blackwell B, Bloomfield SS and Buncher CR (1972) Demonstration to medical students of placebo responses and non‐drug factors. Lancet 1: 1279–1282.

Branthwaite A and Cooper P (1981) Analgesic effects of branding in treatment of headaches. British Medical Journal 282(6276): 1576–1578.

Eccles R (2003) Placebo effects of antitussive treatments on cough associated with acute upper respiratory tract infection. In: Chung KF, Widdicombe JG and Boushey HA (eds) Cough, Causes, Mechanisms and Therapy, pp. 259–268. Massachusetts: Blackwell Publishing Ltd.

Hahn R (1999) The nocebo phenomenon: scope and foundations. In: Harrington A (ed.) The Placebo Effect. An Interdisciplinary Approach, pp. 56–76. Cambridge USA: Harvard University Press.

Luparello T, Lyons HA, Bleecker ER and McFadden ER Jr (1968) Influences of suggestion on airway reactivity in asthmatic subjects. Psychosomatic Medicine 30(6): 819–825.

Further Reading

Evans D (2003) Placebo. The Belief Effect. London: Harper Collins.

Guess HA, Kleinman A, Kusek JW and Engel LW (eds) (2002) The Science of the Placebo. Towards an Interdisciplinary Approach. London: BMJ Books.

Harrington A (ed.) (1999) The Placebo Effect. An Interdisciplinary Approach. Cambridge USA: Harvard University Press.

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How to Cite close
Eccles, Ronald, and Eccles, Khawla Sadiq Jawad(Jan 2006) Placebo Effect. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0004114]