The placebo effect is an improvement in an individual's medical condition or an alleviation of adverse symptoms that occurs when the person receives an inert treatment. It may result from the person's expectation of improvement or from the increased motivation to make improvements in general health that may result. The placebo effect was first described in 1955 by Henry K. Beecher, an American physician, who described it in his frequently cited article, ‘The Powerful Placebo.’ The placebo effect has been explained as a result of the Pavlovian conditioning theory, the expectancy-value theory, and increased motivation on the part of the participant.

A placebo may be contact with a physician, cognitive or behavioral intervention, lifestyle changes in diet or level of physical activity, or a sugar pill. ...