Pain and the Placebo Effect

Healthy volunteers or patients in pain often report less pain after treatment that is inactive, if they believe that the treatment will reduce their pain or other symptoms. The reduction of pain can be partly blocked by the administration of opioid antagonists. Research has also demonstrated reduction in central nervous system activation of pain-relevant areas when individuals were given a placebo but were told it was a painkiller. These findings suggest that a belief or expectation of pain relief generates central nervous system opioid activity that inhibits pain transmission to the cerebral cortex, with a consequent reduction in pain. These effects seem to extend to other symptoms and are implicated in the placebo effect in the context of other regimens. The brain's ability to inhibit pain due to placebo could be conceptualized as a homeostatic system that has evolved to provide protection to the system and enhance the organism's ability to cope.