Adolescent depression treatment pathways in Primary Care – protocol for a longitudinal Cohort Study Describing Naturalistic Flow of Treatment and Evaluating Effectiveness and Cost- effectiveness of Interpersonal Counseling Compared to Treatment as Usual

Background: Implementation of evidence-based interventions is one of the proposed responses to increased demand for treatment of adolescent depression. While the efficacy of interpersonal psychotherapy to treat depression of adolescents (IPT-A) is well established, the effectiveness and cost-effectiveness of the shorter adolescent interpersonal counseling (IPC-A) remains open. Objective: We present a protocol for a prospective evaluation of the naturalistic treatment flow of adolescents with sustained depression, and effectiveness and cost-effectiveness of IPC-A, as compared to treatment as usual or no treatment of sustained depression. Methods: We will collect a prospective cohort of grade 7 to 9 adolescents (13–16-year-olds) in selected Finnish schools using convenience sampling (n=9000). We will compare three groups as defined at 6 months (targeting with IPC-A, n=100; with treatment as usual (TAU), n=200; or no treatment, n=100). The primary outcome measure will be the proportion of adolescents who received specialized psychiatric services by 2 years after baseline. Secondary outcome measures will include longitudinal changes in PHQ-9-A scores by 12 months, positive mental health, social inclusion, and quality of life. Cost-effectiveness will be evaluated using survey data at 12 months, and an economic evaluation using register data and information on service use 12 months before and up to 10 years after baseline. A universal evaluation of all adolescents, independent of mood, will provide prospective description of adolescents a) with sustained depression over the follow-up period (Patient Health Questionnaire 9 items, adolescent version, PHQ-9-A ≥ 10 in two measurements over 6 months), b) with a self-reported need and motivation for support, c) with therapeutic intervention, and d) benefits and harms of treatment. We will describe the treatment received and predictors of treatment and outcome based on reports from adolescents, caretakers, and therapists, as well as electronic patient records. Impact of training in IPC-A on competence and access to treatment will be evaluated. Conclusions: The study will describe need for, pathways to, and content of mental health services for depressed adolescents. The results can improve detection and equal access to care, and inform decision -makers about the best practices for prevention, including utility of the implementation of IPC-A. Trial registration: ClinicalTrials.com NCT06390462 registered 2024-03-19