Platform trial of smartphone-based cognitive–behavioural therapy (CBT) for depressive symptoms among people with no or subthreshold depression: a protocol for the Best, Efficient and Affordable Training in Resilience in Constant Evolution (BEATRICE) platform trial

IntroductionThe global burden of depression continues to rise despite evidence that prevention is feasible and cost-effective. Building on the Resilience Enhancement with Smartphone in Living ENvironmenTs (RESiLIENT) randomised controlled trial, the Best, Efficient and Affordable Training in Resilience in Constant Evolution (BEATRICE) platform trial evaluates and optimises smartphone-delivered cognitive–behavioural therapy (CBT) for adults with no to subthreshold depression. The primary objective is to minimise the Total Burden of Depression, measured by the integral of weekly to monthly Patient Health Questionnaire-8 (PHQ-8) scores over 12 months, through a living, adaptive platform trial that sequentially tests multiple clinical questions and personalised algorithms.Methods and analysisBEATRICE is a nationwide, digitally centralised, multi-arm platform trial conducted via the ‘Resilience Training App’. Eligible participants are adults (aged ≥18 years) with PHQ-8 ≤14, fluent in Japanese, owning a smartphone and not currently receiving mental health treatment. Recruitment takes place through health-insurance associations, companies, municipalities and online outreach. Participants are randomised centrally to CBT skill modules—behavioural activation, assertion training, behaviour therapy for insomnia, cognitive restructuringor problem-solving—delivered alone or in combination. Assessments are open-label and completed digitally by self-reports.The initial list of clinical questions to be examined in this platform trial includes: external validity of the personalised and optimised algorithm for first-line interventions, strategies to help individuals not on track during initial weeks, second-line interventions at 6 months, development of super-personalised and optimised therapy algorithm, that is, longitudinally personalised and optimised in response to individuals’ responses after the first-line assignment. The primary outcomes, sample sizes and statistical analyses differ depending on the clinical question addressed within the platform trial.Ethics and disseminationApproved by the Ethics Committee of Kyoto University Graduate School of Medicine (C1733). Results will be disseminated via peer-reviewed publications, conferences and public reports.Trial registration numberUMIN000058696.