Expectation, the placebo effect and the response to treatment.

What we believe we will experience from a treatment--our expectation--has a substantial impact on what we actually experience. Expectation has been established as a key process behind the placebo effect. Studies in both laboratory and clinical settings consistently show that when people ingest a pharmacologically inert substance (placebo) but believe that it is an active substance, they experience both the subjective sensations and physiologic effects expected from that active substance. Expectation has an important place in the response to "real" treatment as well. This paper provides an overview of the data which point to the role of expectation in both the placebo effect and the response to treatment. These data suggest that clinicians might enhance the benefit of all treatments by promoting patients' positive expectations.