Depression and anxiety are leading causes of disability adjusted life years among adolescents aged 10-19 and can lead to social and educational impairment, substance misuse and suicide. The treatment gap for adolescent mental disorders is large, especially in low-and middle-income countries (LMICs). The WHO Mental Health Gap Action Programme outlines a role for psychological therapies in the treatment of child and adolescent emotional disorders such as depression and anxiety, however there is an urgent need to adapt these for use in LMICs. Between 2018 and 2020, our team including researchers and clinicians from TPO Nepal and King's College London adapted IPT for adolescents with depression in Nepal. Using an iterative mixed methods procedure, we adapted the WHO group IPT manual for delivery by school nurses and lay people in government secondary schools. We conducted an uncontrolled feasibility study of IPT with 62 adolescent boys and girls aged 13 to 19 in the mountainous district of Sindhupalchowk. Adolescents attended 82.3% (standard deviation 18.9) of group sessions. Depression and functional impairment improved between baseline and follow-up at 8-10 weeks post IPT: The Depression Self Rating Scale score decreased by 81% (95% confidence interval 70-95); functional impairment decreased by 288% (249-351).

Building on this previous research, we have designed a 4-stage, 5-year programme of work. The overall aim is to test the effectiveness and cost of scaling-up IPT in Nepal taking a "realist" evaluation approach where we will explore IPT's mechanisms of change and contextual factors that moderate its effects. This involves using formative research to develop an intervention theory of change from which we formulate hypotheses about how intervention mechanisms might interact with context to produce outcomes (context mechanism-outcome configurations, CMOCs).

According to this programme, Stage 1 (Formative Phase) is already completed. Currently we are applying for Stage 2, which is a pilot cluster randomized controlled trial (CRCT-pilot) of IPT for adolescent depression in Chitwan, a district in the lowland region of Nepal. As part of the current application, we aim to 1) test the feasibility and acceptability of the trial protocols, 2) pilot the qualitative and quantitative tools and 3) refine the theory of change hypotheses. Building on it, we will later apply for Stage 3 which will be a full cluster randomized controlled trial assessing the effectiveness/cost-effectiveness of IPT (CRCT-full) and Stage 4 which will consist of testing the CMOs using quantitative data from the full trial.

The study design is a parallel two-arm realist pilot cluster-randomised controlled trial. The trial will be conducted in eight schools (four intervention and four control). We will assess participants in intervention and control arms at baseline (week 0), after the second group session (week 4), after the sixth group session (week 8), at endline (weeks 13-14) and at follow-up (weeks 25-26). The acceptability of the intervention, randomisation, tools, uptake, utility of the intervention, facilitators' fidelity to the manual, mental health outcomes, and cost of design and delivery of the intervention will be assessed. The intervention process data will be also collected. This will include FGDs and interviews with adolescents and their parents, facilitators, nurses, teachers, and school principals to explore feasibility and acceptability of the intervention and study procedures.