The role of placebo effects in immune-related conditions: mechanisms and clinical considerations.

INTRODUCTION: Placebo effects are powerful modulators in clinical outcomes and can either result in treatment benefits or harms, known as placebo and nocebo effects. To harness these outcomes, it is important to focus on the underlying processes that steer these effects, namely by learning through expectations and conditioning. In this review, we focus on the influence of placebo effects on subjective and physiological levels of immune-related conditions (e.g. lymphocyte proliferation, cytokine production or other inflammatory markers). Areas covered: A literature search is conducted in the databases PubMed and PsychInfo by making use of keywords such as 'expectations', 'classical conditioning', 'cytokines', 'immune system', 'learned immunosuppression', and covers studies done in animals, experimental studies in healthy controls as well as studies performed in immune-related patient populations. Expert commentary: We report on the presence of placebo effects in RCTs in immune-related conditions and review findings that demonstrate the ability to learn immune responses in both experimental animal and human placebo studies making use of conditioning paradigms with immunomodulating drug agents. We also discuss results to utilize placebo effects by means of classical conditioning principles in medication regimens for patient populations and elaborate on promising findings of preliminary studies focusing on this topic.