Who responds to placebos? Considering the "placebo personality" via a transactional model.

The placebo effect is now recognised as a genuine psychobiological phenomenon; however, the question of how it can be systematically harnessed to improve health outcomes is not yet clear. One issue that remains unresolved is why some respond to placebos and others do not. A number of traits have been linked to responding, but findings are scattered. In extending prior work, this paper offers three considerations. First, attempts to describe the placebo responder via a single personality trait may be limiting. A synthesis of findings to date suggests placebo responsiveness may reflect a two-faceted construct, with "inward" and "outward" orientation representing the different but related facets of placebo responsiveness. Second, the lack of theoretically driven research may be hindering progress. Personality measures rather than personality theory appear to be driving research and higher order traits are descriptive tools with limited use in predicting behaviour. A biologically based stimulus-response model of personality that considers how individuals respond to certain environmental cues may be more appropriate. Third, a transactional model of placebo responding in which dispositional characteristics interact with environmental contingencies is presented. Responsiveness may manifest in placebo environments where there is a match between an individual's biological trait-like response systems and environmental contingencies. This type of model may be useful in both research and clinical settings. Systematic consideration of how different individuals might respond to different placebo environments might facilitate identification of stable individual characteristics predictive of responding. The ability to determine who is responsive to placebo treatments, and in what context, may enable the matching of individual to treatment, thereby maximising the effectiveness of treatment and minimising possible iatrogenic harm. In the increasingly overtaxed modern health care industry, non-pharmacological treatment alternatives are of critical importance.