New insights into placebo analgesia.

PURPOSE OF REVIEW: The placebo effect is a widespread phenomenon in medicine, both in clinical trials and in routine medical practice. Most of our knowledge about the underlying psychological and physiological mechanisms comes from the study of placebo analgesia. RECENT FINDINGS: When the correct methodological approach is used, striking placebo effects can be detected and these can be mediated by conscious anticipatory processes or unconscious conditioning mechanisms. However, it should be stressed that many improvements observed after the administration of a placebo are not real placebo effects, but different phenomena such as spontaneous remission, regression to the mean and symptom detection ambiguity. Both neuropharmacological studies and brain imaging investigations show that placebo analgesia is mediated by endogenous opioids. Moreover, we also know that during placebo analgesia other systems change their functions, like the respiratory centres and the cardiovascular system. The placebo effect has also been approached from a different perspective by administering analgesics covertly. The results show that hidden medical treatments are less effective than open ones. SUMMARY: The understanding of the placebo effect may lead to better design of clinical trials and better medical practice. For example, it can be used in therapeutic protocols aimed at reducing drug intake.