El efecto placebo, nocebo y precebo en los trastornos funcionales digestivos: ¿imaginación o realidad?

The placebo effect is the therapeutic result derived from the use of a drug, device or inert physical treatment, with which an improvement or change in a subjective malaise or illness is achieved. It is believed that the mechanism of the placebo effect is related to changes of the central nervous system and that, consequently, there are changes at the sensory level and in bodily functions. In the process, an expectation of benefit is generated, although there is no specific effect that changes a specific disorder or, at least, a scientific theory that explains its action. In functional gastrointestinal disorders, the placebo effect is sig-nificant, and it is reported to be present in 6-72% of patients with functional dyspepsia and 0-84% with irritable bowel syndrome. Therefore, it is necessary to have a scientific study of the placebo effect and related effects such as nocebo or precebo. It is important to determine if each of these factors are caused by psychological or neurobiological factors, or if this is a methodological variant that affects the outcome of clinical studies, causing biases in the interpretation of them. This review analyzes the literature and evaluates the psychological and neurobiological mechanisms of the placebo-analgesia, the complexity of the interaction and its evaluation, since the term placebo is not limited to the use of inert substances.