Effectiveness and implementation of the SHIELD integrated multi-level model to reduce adolescent depression and internet addiction: A cluster randomized waitlist-controlled trial in Wang Chin district, Phrae province

Abstract

Background: Adolescent depression and internet addiction are substantial comorbid mental health challenges in rural Thailand, where access to evidence-based interventions remains limited. Traditional single-modality approaches often fail to address the complex interplay among individual, family, and systemic factors that contribute to these conditions.

Objectives: This study aimed to evaluate the effectiveness and implementation outcomes of the SHIELD (Screening & surveillance, Health literacy enhancement, Internet wellness program, Empowering families, Linkage to care, Data-driven monitoring) integrated multi-level intervention for reducing depression and internet addiction among at-risk adolescents in rural Thailand.

Methods: A cluster-randomized waitlist-controlled trial was conducted across eight secondary schools in the Wang Chin district, Phrae province, between October 2024 and June 2025. The schools were randomized to immediate intervention (n = 4) or waitlist (n = 4) control groups. Participants included 240 at-risk students aged 12–18 years with Patient Health Questionnaire-9 (PHQ-9) ≥ 5 and Internet Addiction Test (IAT) ≥ 40. The 12-week SHIELD intervention integrated digital screening, psychoeducation, family therapy, internet wellness training, care coordination, and real-time monitoring, which was delivered by trained registered nurses, school counselors, and clinical psychologists. Primary outcomes included depression severity (PHQ- 9) and internet addiction levels (IAT). The secondary outcomes included mental health literacy, family functioning, quality of life, and implementation metrics using the RE-AIM framework. The observed intracluster correlation coefficient was 0.048. Data were analyzed using intention-to-treat mixed-effects models accounting for clustering, with economic evaluation performed from a societal perspective.

Results: At 6-month follow-up, the intervention group demonstrated significantly greater improvements in PHQ-9 scores (mean difference: −3.1, 95% CI: −4.0 to −2.2,P < 0.001, Cohen’s d = 0.68) and IAT scores (mean difference: −11.2, 95% CI: −14.8 to −7.6,P < 0.001, d = 0.67) compared to controls. Moreover, the clinical response rates (≥ 50% PHQ-9 reduction) were 64.8% vs. 25.5% (OR = 5.4, 95% CI: 3.2–9.2, NNT = 3) and the remission rates (PHQ-9 < 5) were 35.2% vs. 11.8% (OR = 4.1, 95% CI: 2.1–8.0, NNT = 5) differed between the intervention and control groups, respectively. Subgroup analyses demonstrated consistent intervention benefits across sex and age groups, with greater effects observed among students with moderate-to-severe baseline depression (d = 0.81) than mild depression (d = 0.54). Furthermore, the secondary outcomes revealed significant improvements in mental health literacy (d = 0.78), family functioning (d = 0.52), and quality of life (d = 0.40). The implementation outcomes demonstrated high fidelity (88.4%), excellent adoption (100.0% school participation), and favorable cost-effectiveness (ICER = 12,830 THB per depression-free year, below the WHO threshold of 34,400 THB).

Conclusion: The SHIELD integrated multi-level intervention exhibited substantial and sustained effectiveness in reducing adolescent depression and internet addiction with excellent implementation outcomes and favorable cost-effectiveness. Despite real-world implementation challenges, including initial barriers to parental engagement and technology access in rural settings, high fidelity was maintained throughout the trial. These findings support the potential for scaling evidence-based, culturally adapted interventions within Thailand’s educational and mental health systems to address the growing adolescent mental health needs in resourceconstrained settings.