The role of psychological mechanisms in the treatment process cannot be underestimated,
the well-known placebo effect unquestionably being a factor in treatment. However,
there is also a dark side to the impact of mental processes on health/illness as exemplified
by the nocebo effect. This phenomenon includes the emergence or exacerbation of negative
symptoms associated with the therapy, but arising as a result of the patient's expectations,
rather than being an actual complication of treatment. The exact biological mechanisms
of this process are not known, but cholecystokinergic and dopaminergic systems, changes
in the HPA axis, and the endogenous secretion of opioids are thought to be involved.
The nocebo effect can affect a significant proportion of people undergoing treatment,
including cancer patients, leading in some cases to the cessation of potentially effective
therapy, because of adverse effects that are not actually part of the biological effect
of treatment. In extreme cases, as a result of suggestions and expectations, a paradoxical
effect, biologically opposite to the mechanism of the action of the drug, may occur.
In addition, the nocebo effect may significantly interfere with the results of clinical
trials, being the cause of a significant proportion of complications reported. Knowledge
of the phenomenon is thus necessary in order to facilitate its minimalization and
thus improve the quality of life of patients and the effectiveness of treatment.