The demand for prevention and treatment of adolescent depression has rapidly increased over years. A national project to improve treatment of adolescent depression in primary care has taken place in Finland starting 2020.

The goal of this prospective observational cohort study is to describe pathways to mental health services in adolescents with depressive symptoms. The main questions it aims to answer are:

• Do young people reporting depressive symptoms have equal access to treatment?
• How is it best to recognize those adolescents who will benefit from IPC-A?

Adolescents who participate in the study will

• complete a survey on protective and risk factors of depression three times over 6 months
• report possible depressive symptoms every two weeks over 6 months
• report whether they needed and received help, motivation for treatment, and benefits and harms from treatment

We will also collect

• information from one of caretakers with two surveys within 6 month- intervals on their view on adolescent's need for support, strengths and risks, and benefits and harms from treatment where applicable
• where applicable, from the professional who provided support after the intervention on their training and competence, as well as content of and response to treatment
• register data to estimate overall provision and cost of social welfare and health care services one year preceding the study and over 2 to 10 years after the observation period

Researchers will compare an intervention that is new in Finland, adolescent interpersonal counseling (IPC-A), to other treatments of depression, to see if it is equal to or better than other treatments of depression.

Background: Implementation of evidence-based interventions is one of the proposed responses to increased demand for prevention and treatment of adolescent depression. A national implementation of adolescent interpersonal counseling (IPC-A) has taken place in Finland starting 2020. While the efficacy of interpersonal psychotherapy (IPT-A) as an intervention to treat depression of adolescents is well established, the effectiveness and cost-effectiveness of the shorter adaptation, IPC-A, remains open. Investigators present a protocol for an evaluation of pathways to mental health services of depressed adolescents and a prospective, observational community-based cohort study to estimate the effectiveness and cost-effectiveness of IPC-A, as compared to adolescents with sustained depression with treatment as usual or no treatment.

Methods: The cohort will include grade 7 to 9 adolescents (13-16-year-olds) in selected Finnish schools, excluding adolescents with preceding treatment of depression. A universal prospective evaluation of adolescents in a 6-month follow-up will provide information on the proportion of adolescents a) with sustained depression over the follow-up period (Patient Health Questionnaire 9 items, PHQ-9 ≥ 10) in two measurements over 6 months), b) with a self-reported need for support due to depressive symptoms, and c) with a therapeutic intervention. The investigators will describe the treatment received (number of sessions, therapeutic content) based on reports from adolescents, caretakers, and therapists, as well as electronic patient records. The primary outcome measure will be the proportion of adolescents who will receive specialized psychiatric services by 12 months after baseline. Secondary outcome measures comparing three groups as defined at 6 months (IPC-A, treatment as usual (TAU), or no treatment group). They will include proportion of adolescents who received any support by 12 months after baseline, and longitudinal changes in PHQ-9-A scores by 12 months. 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 2 and 10 years after baseline. Collection of survey data is expected to start in March 2024 and is set to finish in May 2025.

Discussion: The study will describe need for, pathways to, and content of social and health services for depressed adolescents. Benefits and harms of treatment and the national implementation will be observed. 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.

Inclusion Criteria:

• we will include all adolescents attending grades 7 to 9 in selected schools with on informed consent

Exclusion Criteria:

• psychiatric care within the past 12 months or receiving a psychosocial intervention (psychotherapy, IPC-A, any other therapy of support) during the 12 months before baseline,
• an inability to reliably understand the Finnish, Plain Finnish, Swedish, or English versions of the survey, or
• an adolescents' or caretakers' report of a need for exclusion, such as another medical condition - including a mental disorder - requiring acute current treatment or support.

Adolescents attending grades 7 to 9 (13 to 16 years) in selected schools

Mauri Marttunen and Klaus Ranta: effectiveness and psychometrics; Johanna Lammintakanen: cost-effectiveness and economic evaluation; Jari Lahti: motivation to treatment; Erkki Heinonen: Therapist competence and outcome

First baseline IPD available from fall 2025 for 10 years, final economic evaluation data will be stored from 2039 for 10 years

Data access is restricted by user roles with permission of PI (Outi Linnaranta), and all data will be pseudonymized. Sensitive register data including person IDs will be managed using the Findata Kapseli service.