Rethinking placebo in psychiatry: the range of placebo effects

Summary This article, the first of two on placebo effects, provides a broad overview of placebo in the field of medicine. A brief conceptual history is followed by some basic facts about placebos. Problems of definition are identified. Additive and non-additive models of treatment effects, and problems of measurement of placebo effects are described. The role of placebo in the pharmacotherapy of depression and complementary and alternative medicine is discussed. The ‘efficacy paradox’ (that placebo treatments can have larger effects than ‘evidence-based treatments’) is introduced. Finally, ethical issues are discussed.