Placebo, nocebo, and psychogenic illness

Abstract

Psychogenic diseases are attributable to a variety of psychological and social factors that may trigger the onset of symptoms and influence the course of the disease. Whenever psychological factors are involved, both placebo effects and their evil twins, nocebo effects, play an important role. These involve a number of mechanisms, ranging from expectation, anxiety, reward to learning phenomena, such as Pavlovian conditioning, cognitive and social learning. There is also some evidence of different genetic variants in placebo responsiveness, and these give rise to high response variability.