ABSTRACT
Psychotherapy draws on common factors such as the generation of hope and positive feeling as part of its process. Because of this, it remains vitally important to sort out whether a treatment is effective because of something special about the treatment or simply because it invokes such common factors. This chapter looks at what research can tell us about placebo effects. Placebos are usually defined as treatment-like interventions that evoke patients' expectations of improvement despite lacking any active ingredient specifically intended to affect a particular disorder. Just as a placebo pill may look and feel like medicine but contain only sugar, placebo therapy looks like therapy—it may involve two people talking—but it entails no intervention designed to have an effect on the problem at hand. In medicine, placebos have been assumed to have a marked impact on health since 1955, when Henry Beecher, in a milestone review of 15 studies, documented their effect.
