Bayesian randomised controlled trial of guided parent-delivered cognitive behavioural therapy for children with anxiety disorders via remote sessions in Japan: a study protocol

Introduction Guided parent-delivered cognitive behavioural therapy (GPD-CBT) is an evidence-based, low-burden treatment programme for childhood anxiety disorders with demonstrated efficacy, cost-effectiveness and accessibility. However, it has been tested primarily in Western countries, and the efficacy and cost-effectiveness have not been evaluated in Japanese families. The current study aims to examine GPD-CBT’s efficacy and cost-effectiveness in Japanese samples and explore potential cultural adaptations of the programme. Method and analysis This study is designed as a Bayesian single-blind randomised controlled trial with two parallel groups: GPD-CBT (intervention group) and a waitlist control group. The primary outcome is remission of primary anxiety disorders evaluated through diagnostic interviews by independent evaluators. Secondary outcomes include child and parent-reported child anxiety symptoms, depressive symptoms and life interference. Additionally, measures of parental psychological characteristics, programme acceptability and quality of life are collected. We will conduct qualitative interviews with parents who participated in the programme and therapists who delivered the intervention to explore potential cultural adaptations. We aim to recruit 54–170 families, depending on the results of sequential Bayesian analyses. GPD-CBT consists of seven weekly 20 min sessions and a 1-month follow-up session. Assessments will be conducted at baseline, 13 weeks post randomisation (primary endpoint for between-group comparison), with an additional 25 weeks post randomisation. The waitlist control group will receive GPD-CBT after the 13-week assessment. Ethics and dissemination This study has been approved by the Ethics Review Committees of Chiba University and the University of Tokyo. We will disseminate results through academic conference presentations and peer-reviewed journal publications. If the GPD-CBT intervention proves efficacious, we will promote wider implementation in Japan through the development of training programmes for mental health professionals and key stakeholders. Trial registration numbers jRCT1032250421 ( https://jrct.mhlw.go.jp/latest-detail/jRCT1032250421 ) and jRCT1030250422 ( https://jrct.mhlw.go.jp/latest-detail/jRCT1030250422 ) registered on 9 October 2025.