The placebo effect revisited: lessons learned to date.

This article summarizes six lessons that can be learned from over a half century of scientific research on the placebo effect. These lessons are that the placebo response is not the placebo effect, it is meaningless to ask what the magnitude of the placebo effect is, it is easy to be fooled by regression artifacts, expectancy and conditioning are not conflicting processes that can be pitted against each other, some of our questions can be answered by history, and the outcomes of active treatments can be enhanced by attention to placebo components.