The nocebo phenomenon: concept, evidence, and implications for public health.

The nocebo hypothesis proposes that expectations of sickness and the affective states associated with such expectations cause sickness in the expectant. The nocebo phenomenon is a little-recognized facet of culture that may be responsible for a substantial variety of pathology throughout the world. However, the extent of the phenomenon is not yet known, and evidence is piecemeal and ambiguous. This paper reviews the concept of nocebo and its association with the placebo phenomenon, gives examples of evidence for the nocebo phenomenon, and suggests public health implications.