Conditioned open-label placebos to facilitate opioid reduction in patients with chronic non-cancer pain: study protocol of a randomised controlled trial.

Introduction: Chronic non-cancer pain presents a global health problem, with a significant increase in opioid prescriptions over recent decades. However, opioid therapy poses risks of adverse events, overdose and non-medical use. As a result, many patients seek to discontinue or reduce their opioid intake. Strategies for opioid tapering often lack efficacy, prompting the investigation of novel approaches like open-label placebo (OLP), that is, the administration of a placebo with full disclosure that it is a placebo. OLP has shown efficacy in chronic non-cancer pain syndromes and has been suggested as a promising candidate for medication tapering. This study aims to assess whether OLPs can enhance the reduction of daily morphine equivalent dose (MED) in chronic non-cancer pain patients and examines its potential in mitigating opioid withdrawal symptoms.

Methods and analysis: This study is designed as a randomised, controlled, single-centre trial. Participants will be randomised into either an OLP group or a control group. The study duration will span six to nine weeks, during which all participants will aim to reduce their opioid intake. Both groups will monitor their opioid intake daily using a diary app and will receive feedback on their progress of reducing opioids. Additionally, participants in the OLP group will receive OLP tablets for the entire study period. During the first week, the OLP group will undergo a one week learning phase using a classical conditioning paradigm, where each opioid intake is paired with a placebo. In the subsequent five weeks, the OLP group will enter a dose-extension phase in which only the first opioid intake of the day is paired with a placebo, and additional placebos can be taken as desired. At the end of the study, qualitative interviews will be conducted with the first 15 participants in the OLP group. The primary outcome measure is daily opioid intake. Secondary outcomes include opioid withdrawal symptoms, pain severity, disability, anxiety, depression, opioid beliefs, intervention expectancy and qualitative data. Statistical analyses will include analysis of covariance and regression models.

Ethics and dissemination: The ethics committee of the Canton of Zurich, Switzerland, approved the study (SNCTP-nr.: SNCTP000005853/BASEC nr.: 2023-02327).Participants will be compensated with 100 Swiss Francs for their full participation in the study. Participants who will take part in the qualitative interview will be compensated with additional 15 Swiss Francs.

Trial registration number: This study is registered at clinicaltrials.gov: NCT06350786.