A placebo is a sham medical intervention. In one common placebo procedure, a patient is given an inert sugar pill, told that it may improve his/her condition, but not told that it is in fact inert. Such an intervention may cause the patient to believe the treatment will change his/her condition; and this belief does indeed sometimes have a therapeutic effect, causing the patient's condition to improve. This phenomenon is known as the placebo effect.
Placebos are widely used in medicine, and the placebo effect is a pervasive phenomenon; in fact, it is part of the response to any active medication. However, the deceptive nature of the placebo creates tension between the Hippocratic Oath and the honesty of the doctor-patient relationship. The placebo effect points to the importance of perception and the brain's role in physical health.
Since the publication of Henry K. Beecher's The Powerful Placebo in 1955 the phenomenon has been considered to have clinically important effects. This view was notably challenged when in 2001 a systematic review of clinical trials concluded that there was no evidence of clinically important effects, except perhaps in the treatment of pain and continuous subjective outcomes. The article received a flurry of criticism, but the authors later published a Cochrane review with similar conclusions. Most studies have attributed the difference from baseline till the end of the trial to a placebo effect, but the reviewers examined studies which had both placebo and untreated groups in order to distinguish the placebo effect from the natural progression of the disease.
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