Historically, the concepts of the placebo and the placebo effect have been quite broad; only recently have these concepts been narrowed to become virtually synonymous with the administration of inert medications. In the last three decades, investigators have sought to define the conditions under which the placebo effect operates. The 1950's saw the widespread use of placebo medication as controls in the evaluation of drug effects. A major conclusion from these studies was not only that placebos are indispensable as controls in scientific drug evaluation, but also that placebos are powerful therapeutic tools in themselves. Investigators also expressed the hope that psychological tests and personality profiles could identify those individuals who would react to placebos.
This earlier optimism that individual placebo reactors existed and could consistently be identified was not justified. Subjects and patients responded inconsistently to inert medication, reacting under certain therapeutic situations and stimuli but not under others. Many investigators began to view