Mechanism of Placebo-Induced Analgesia

Placebo's are often referred to as an inert substance or treatment and a placebo effect is merely considered as a psychologically suggestive effect which is assumed to be an important component of any medical and (psycho)-therapeutic treatment. Placebo effects related to pain control have also been observed. An interesting and also important question is what possible biological endogenous substrate can explain the self-healing effect in placebo analgesia. In reviewing the empirical evidence of the hypothesis that endorphins are responsible for the analgesic effect of placebo, most of the clinical and experimental pain studies into the mechanism of placebo-induced analgesia seem to support this hypothesis. In presuming that endorphins may mediate the analgesic effect of placebo, future research should elucidate how the self-healing effect of placebo, reflected by the release of endorphins, could be optimized. Two psychological models (conditioning model and expectancy model) may offer a lead for further research.