The Placebo Effect: A Neurobiological Review

Abstract

The placebo effect is currently understood as a psychosocial and neurobiological interaction in which individuals’ expectation of effective treatment initiates a biological response to facilitate symptomatic relief. In this review, the literature describing the placebo effect in experimental and clinical pain is synthesized. The various methods of inducing placebo, including verbal suggestion, social cues, expectancy manipulations, open/hidden administration, and classical conditioning are included. Both opioid and non-opioid placebo mechanisms are explored based on studies using naloxone and proglumide to investigate opioid presence. Finally, an overview of neuroimaging studies is presented in which positron emission tomography, event-related potential, and functional magnetic resonance imaging findings are discussed. Conclusions and implications of the studies reviewed are presented at the end.