Home > Encyclopedia of Psychology > Placebo Effect

In research, a scientifically significant response that cannot be explained by physiological variables and is assumed to be psychological in origin.

Placebos are substances with no known pharmacological value that are given to members of a control group in an experiment. In studies determining the effectiveness of a particular drug, for example, the experimental group is given the drug being studied and the control group is given a placebo, which is made to look exactly like the actual drug. Neither group, nor the researchers, knows which received the drug and which the placebo. If the members of each group show similar responses, the placebo effect has been produced. For reasons not completely understood, the patients given the placebo have...