Mechanisms of the Placebo Response
A placebo is characterized as a pharmacological ineffective ingredient or a treatment with unspecific effect. The placebo response is the positive effect that is caused by this nonspecific ingredient or treatment. The placebo response is mediated primarily via distinct but interrelated mechanisms: cognitive factors such as patient expectations of the benefit of a treatment, the quality of patient-doctor relationship and associative learning (conditioning) processes. Correspondingly, the terms nocebo response/nocebo effect refers to negative effects that are caused by nonspecific treatment ingredients or treatments, steered by mechanisms similar to those responsible for the placebo response. In a broader sense, nocebo effects are also assumed if a patient believes to suffer from a disease that is not present, or in case of a misdiagnosed disease.
The most recent scientific knowledge documents not only the neuropsychological and neurobiological mechanisms behind the placebo/nocebo response in more and more details but also identifies factors and predictors causally responsible for the placebo/nocebo response. Based on this knowledge and the specific application of these predictors the placebo/nocebo response can be controlled. On the one hand, this insight provides the unique opportunity to maximize the efficacy of therapeutical interventions for the patient benefit, or – in case of nocebo effects – these to avoid. On the other hand, it offers potential implications for the design of clinical and pharmacological trials by controlling and restricting the placebo effect with the aim being to optimize the quantification of the test substance or treatment.