BACKGROUND: Adolescent depression is a common mental health problem and there is an urgent need for effective and accessible treatments. Internet-based interventions solve many obstacles for seeking and receiving treatment, thus increasing access to effective treatments. Internet-based cognitive behavioural therapy (ICBT) for adolescent depression has demonstrated efficacy in previous trials. In order to broaden the range of evidence-based treatments for young people, we evaluated a newly developed affect-focused Internet-based psychodynamic treatment (IPDT) in a previous study with promising results. The purpose of the planned study is to evaluate the efficacy of IPDT for adolescent depression in a non-inferiority trial, comparing it to ICBT.

METHODS: The study will employ a parallel randomized non-inferiority design (ratio 1:1; n = 270). Eligible participants are adolescents 15-19 years suffering from depression. The primary hypothesis is that IPDT will be non-inferior to ICBT in reducing depressive symptoms from pre-treatment to end of treatment. Secondary research questions include comparing outcomes of IPDT and ICBT regarding anxiety symptoms, emotion regulation and self-compassion. Additional data will be collected to evaluate cost-effectiveness as well as investigating predictors, moderators and mediators of outcome. In addition, we will examine long-term outcome up to 1 year after end of treatment. Diagnostic interviews with MINI 7.0 will be used to establish primary diagnosis of depression as well as ruling out any exclusion criteria. Both treatments consist of eight modules over 10 weeks, complemented with therapist support through text messages and weekly chat sessions. Primary outcome measure is the Quick Inventory of Depressive Symptomatology in Adolescents Self-Rated (QIDS-A17-SR). Primary outcome will be analysed using data from all participants entering the study using a multilevel growth curve strategy based on the weekly measurements of QIDS-A17-SR. The non-inferiority margin is defined as d = 0.30.

DISCUSSION: This trial will demonstrate whether IPDT is non-inferior to ICBT in the treatment of adolescent depression. The study might therefore broaden the range of evidence-based treatment alternatives for young people struggling with depression. Further analyses of data from this trial may increase our knowledge about "what works for whom" and the pathways of change for two distinct types of interventions.

TRIAL REGISTRATION: ISRCTN12552584 , Registered on 13 August 2019.