The placebo effect on mood and behavior: possible role of opioid and dopamine modulation of the hypothalamic-pituitary-adrenal system.

There has been an increasing interest in the placebo effect over the past several decades. The relationship between the placebo effect and the underlying mechanisms of the body that control and maintain health is still not well understood. Significant evidence suggests that endogenous opioids and dopamine are involved in the mechanisms of the placebo effect. The endogenous opioid and dopaminergic systems have been demonstrated to exert effects on the functional activity of the hypothalamic-pituitary-adrenal (HPA) axis. The HPA system contributes to regulation of mood and behavior. The author suggests that opioid and dopamine modulation of the HPA system is one of the neurobiological mechanisms of the placebo effect on mood and behavior. To elucidate the underlying biological mechanisms of placebo effects and to study the use of placebo in clinical practice to improve health are two important and interrelated tasks. Future studies of the neurobiology of the placebo response may yield interesting and important results. Copyright 2003 S. Karger GmbH, Freiburg