Rethinking placebo in psychiatry: how and why placebo effects occur

Summary This article outlines proximate (physical and mental) and ultimate mechanisms of placebo effects. Interpersonal processes contributing to placebo effects are reviewed and illustrated through research into the process of psychotherapy. Evolutionary theories of how and why the capacity for placebo effects might have evolved are described. The components of treatment and placebo effects are defined. It is concluded that maximising therapeutic placebo effects is effective and a valid clinical goal.