Long-term effects of psychosocial interventions for adolescents on depression and anxiety: a systematic review and meta-analysis

Background: Adolescence represents a distinctive phase of development, and variables linked to this developmental period could affect the efficiency of prevention and treatment for depression and anxiety, as well as the long-term prognosis. The objectives of this study were to investigate the long-term effectiveness of psychosocial interventions for adolescents on depression and anxiety symptoms and to assess the influence of different intervention parameters on the long-term effects. Methods: In this systematic review and meta-analysis, we searched five databases (Cochrane Library, Embase, Medline, PsychInfo, Web of Science) and trial registers for relevant papers published between database inception and Aug 11, 2022, with no restrictions on the language or region in which the study was conducted. An updated search was performed on Oct 3, 2023. Randomised controlled trials of psychosocial interventions targeting specifically adolescents were included if they assessed outcomes at 1-year post-intervention or more. The risk of bias in the results was assessed using the Cochrane RoB 2.0. Between-study heterogeneity was estimated using the I² statistic. The primary outcome was depression and studies were pooled using a standardised mean difference, with associated 95% confidence interval, p-value and I². The study protocol was pre-registered on PROSPERO (CRD42022348668). Findings: 57 reports (n = 46,678 participants) were included in the review. Psychosocial interventions led to small reductions in depressive symptoms, with standardised mean difference (SMD) at 1-year of −0.08 (95% CI: −0.20 to −0.03, p = 0.002, I² = 72%), 18-months SMD = −0.12, 95% CI: −0.22 to −0.01, p = 0.03, I² = 63%) and 2-years SMD = −0.12 (95% CI: −0.20 to −0.03, p = 0.01, I² = 68%). Sub-group analyses indicated that targeted interventions produced stronger effects, particularly when delivered by trained mental health professionals (K = 18, SMD = −0.24, 95% CI: −0.38 to −0.10, p = 0.001, I² = 60%). No effects were detected for anxiety at any assessment. Interpretation: Psychosocial interventions specifically targeting adolescents were shown to have small but positive effects on depression symptoms but not anxiety symptoms, which were sustained up to 2 years. These findings highlight the potential population-level preventive effects if such psychosocial interventions become widely implemented in accessible settings, such as schools. Future trials should include a longer term-follow-up at least at 12 months, in order to determine whether the intervention effects improve, stay the same or wear off over time. Funding: UKRI Medical Research Council.