Study design
RA
BLIND
We performed a cluster-randomized controlled trial in primary care, including patients who had been using ADM for at least nine months who wished to discontinue. Allocation in a 1:1 ratio was performed at the level of the GP practice to avoid contamination and to simplify research procedures for GPs and mental health nurses. Generation of the numbers for the randomization schedule was performed by a statistician (RA), based on block randomization with blocks of two, stratified for region (north, central and east Netherlands) and type of practice (single versus group). Allocation was performed by the researcher (CW) in collaboration with the statistician who consecutively allocated practices to the randomization scheme. Patients, GPs, and the research team were aware of treatment allocation. The mental health nurses were kept blind to allocation to ensure that SPD was offered in the same way to all participants, and both GPs and patients were asked not to reveal this information. The study was approved by the medical-ethical committee Arnhem-Nijmegen (2016–2527) and all patients gave written informed consent before entering the intervention phase of the study.