Placebo

Placebo, in medicine, an inert substance, such as sugar, that is used in place of an active drug. In testing new drugs, placebos are used to avoid bias. That is, in a blind test, patients do not know if they have been given the active drug or the placebo; in a double-blind test, physicians observing the results also do not know. Placebos may be administered to some patients who have incurable illnesses in order to induce the so-called placebo effect: an improvement, at least temporarily, of the patient's condition. In a 1955 study by the American anesthesiologist Henry Knowles Beecher, the condition of 35 percent of more than 1000 patients tested was improved by administering placebos. Little is understood of how this effect works, but one theory is that the patient's faith in a cure may be related to the release of brain chemicals called endorphins, the body's natural opiates. The effect may be negative, however, if hopes have been raised too high.