Conditioning, expectation, and desire for relief in placebo analgesia

The factors that contribute to the magnitude of placebo analgesia have, until recently, been elusive. This review explores the roles of external factors, such as conditioning, and experienced factors, such as expectation and desire for pain reduction, in placebo analgesia. Placebo analgesia effects have been found to reflect decreases in pain beyond that accounted for by the natural history of a pain condition. These effects clearly are influenced by the effectiveness of previous active treatments (ie, conditioning) as well as by environmental factors that provide cues/suggestions for analgesia. However, external factors are effective insofar as they provide expectations for pain reduction and a lowering of desire for relief. Experienced factors, such as expectation and desire for relief, also are integral dimensions of some human emotional states, such as anxiety. We present an explanation of placebo analgesia that suggests that it is the result of mechanisms that also regulate emotional states.