Placeboresponsen

Placeboresponsen, often translated as placebo response, refers to the improvement in health or symptoms observed after administration of an inert treatment. This improvement cannot be attributed to the physical pharmacology of the substance and is instead influenced by contextual and psychological factors, such as the patient’s expectations, the clinician-patient relationship, and conditioning from prior treatments. Distinctions between placebo response and placebo effect are sometimes subtle; some researchers reserve placebo effect for the average change caused by placebo in a controlled trial, while placebo response includes all changes observed in the placebo arm, including natural disease progression. In practice the terms are often used to mean the same phenomenon.

The placebo response arises from brain mechanisms that generate expectation and reward, involving endogenous opioids, dopamine, and other neurotransmitter systems; activity changes have been observed in pain-modulation networks, the prefrontal cortex, and limbic circuits. Conditioning and repeated treatment rituals can strengthen responses.

Most robust evidence exists for analgesia, but placebo responsiveness is seen in mood disorders, irritable bowel syndrome, Parkinson’s disease, and other conditions. Predictors include prior positive treatment experiences, optimism, trust in the clinician, and genetic factors; age and sex can influence responsiveness, and individual differences are substantial.

In clinical trials, placebo response can complicate the assessment of treatment effects; in practice, clinicians may harness it through careful communication and supportive care, and open-label placebo studies show benefits even when patients are told they are receiving a placebo. Negative expectations can produce nocebo effects.