Placebo effect

The placebo effect is an effect of a medical treatment that is attributable to an expectation that the treatment will have an effect, i.e., the effect is due to the power of suggestion. Thus the placebo effect can have a true physiologic role as a component of the effect of a treatment.

Formally, it is "an effect usually, but not necessarily, beneficial that is attributable to an expectation that the regimen will have an effect, i.e., the effect is due to the power of suggestion." This means that an active drug or intervention has additional effects, or even the suppression of side effects, due to suggestion by the clinician.

The word placebo was first used in conjunction with medical treatments by William Cullen in the 18th century. Cullen, the leading physician of the day, used it to describe treatments that he gave with the intention of reassuring the patient rather than with any rational expectation that they might be effective through objective physiological mechanisms.

However, for very many conditions, it is now clear that the placebo effect can be very powerful indeed. In 1955, researcher H.K. Beecher published "The Powerful Placebo," in which he concluded that, across 26 studies he analyzed, an average of 32 percent of patients responded to placebo. In the 1960s, many studies showed physiological effects of dummy pills--they tended to speed up pulse rate, increase blood pressure, and improve reaction speeds, for example, when participants were told they had taken a stimulant, and had the opposite effects when participants were told they had taken a sedative.

In the first decade of the 21st century, there was an explosion of research into the placebo effect, as brain imaging technology made it possible to visualise, in human volunteers, the brain activity underlying the placebo effect.