Wirkmechanismen des Placeboeffekts - Nutzen und Anwendbarkeit in medizinischen Behandlungen

This work is dedicated to the investigation of placebo mechanisms as well as to their applicability and possible benefits in medical treatments. The expectancy of patients on their treatment has proven to be a central placebo mechanism in the treatment of different medical conditions, especially for acute pain. However, it must be assumed that the influence of expectancy varies between different symptoms. Thus, experimental evidence is necessary for additional patient groups. Besides the patients’ expectancy, the physician‒patient relationship represents another placebo mechanism, but, up to day, no consistent framework exists for the heterogeneous communication aspects, which have been investigated in this context. A classification of communication styles (doctor-centered vs. patient-centered), which is common in other research areas, could also be adapted to investigate placebo effects. When placebo interventions are applied in clinical practice, which is done by most physicians on a regular basis, the mechanisms of expectancy and physician–patient relationship are used to induce beneficial placebo effects. However, the deception involved in the placebo application disagrees with ethical standards. Open-label placebos (OLPs), i.e. placebos prescribed honestly, might solve this ethical problem and have already proven effective for the treatment of different symptoms. Based on these findings, the following thesis presents experimental studies on the two mentioned placebo mechanisms, i.e. patients’ treatment expectations and physician‒patient communication. The studies are briefly summarized below. According to meta-analyses, placebo effects and treatment expectancy were found to have a large impact in the pharmacological treatment of depression. However, to use these effects, specific experimental evidence is crucial. Therefore, a first experimental study investigates whether the application of a placebo is capable of counteracting a sadness induction in clinically depressed patients (N = 94) and which role the participants’ expectations towards the placebo play. The results reveal that taking the placebo with the expectation to receive a fast-acting antidepressant reduces the patients’ sadness, although sadness is induced experimentally. The effects are found to be much larger than in a corresponding pilot study with healthy participants. In a second experimental trial, a standardized interaction between provider and patient is developed in accordance with the mentioned classification of communication styles and is implemented in an experimental placebo paradigm. This constitutes a basic research step enabling future studies to investigate physicians’ communication styles in the context of placebo effects. Initially, the influence of the two different communica¬tion styles on healthy participants’ willingness to take a medication is investigated. After receiving a medical consultation with a patient-centered communication style, participants intention to take a performance-enhancing medication before performing a concentration test is significantly increased compared to the intention of participants who did not receive a consultation. To examine the applicability of placebo treatment complying with ethical standards of health care, an online vignette-study on a large sample of the German lay population (N = 798) is presented. Participants express higher outcome expectations towards a deceptive placebo (DP) to treat a sleeping disorder than towards an OLP. Surprisingly, they also rate the DP as more acceptable than the OLP, although the first comprises a deception. In summary, this thesis provides experimental evidence addressing the applicability and benefits of placebo mechanisms to optimize medical interventions. By inducing positive expectations, large placebo effects can be caused in patients with major depression. Furthermore, the findings show that the communication style of health care providers plays a major role on healthy persons’ intention to take a medication. However, to implement open-label placebo treatments in daily health care, the acceptance towards such interventions in the general population should be further increased.