Placebo Effect

Abstract

Placebos are commonly used in clinical trials to validate the efficacy of a therapy. The term placebo refers to the whole ritual of the therapeutic act, embracing both the inert substance and the psychosocial context around the patient and the therapy. Placebos represent an excellent model to understand different brain functions and the way mental activity may affect several physiological processes. Many placebo effects exist, with different mechanisms across different medical conditions and therapeutic interventions. Expectation, anxiety, and reward are all involved, as well as a variety of learning phenomena and genetic variants. At present, the most productive models to better understand the psychobiology of the placebo effect are pain, motor and mental disorders, the immune and endocrine systems, and fatigue. Healing context aside, placebo effects are also crucial for physical and cognitive performance. These models have provided compelling evidence that different social stimuli, such as words and therapeutic rituals, may change the patient's brain, and these effects are similar to those induced by drugs. In light of these considerations, we are today in a good position to investigate complex psychological factors like placebo effects and the doctor-patient relationship by using both a physiological and a neuroscientific approach. The translational implications of this new knowledge range from clinical trial design to medical practice to social and ethical issues.