ABSTRACT
One of most common effects in research and clinical practice is the placebo effect characterized by experienced changes in symptoms in response to a perceived trigger. This chapter begins with common understandings of the term "placebo", how it is used in research as a control, and how it is employed clinically when no other treatment is available. It identifies physician and patient factors, and illustrates the power of suggestion and its physiological effects. The chapter describes the psychological characteristic of environmental illness (EI) patients who are most vulnerable to the suggestion of illness in terms of somatization and somatoform disorders. Provocation challenges have been used throughout history, long before toxicology became a science, and long before double-blind, placebo-controlled studies became the "gold standard" for identifying environmental intolerances. Many valid psychological mechanisms have been hypothesized to explain the placebo effect, including belief, expectation, faith, hope, suggestion, transference, and conditioning.
