To Örebro University

Introduction: Adolescent mental health problems represent a significant global health issue, particularly in low- and middle-income countries, such as the Republic of North Macedonia and the Republic of Moldova. Effective and scalable interventions are urgently needed to address these challenges.

Methods and analysis: This protocol outlines a multicountry cluster randomised factorial trial, implemented according to the multiphase optimisation strategy (Phase 2), which evaluates the effectiveness and costs of three add-on components for the Parenting for Lifelong Health for Parents and Teens programme: adolescent mental health tools based on UNICEFs Helping Adolescents Thrive comics, adolescent peer support based on UNICEFs ‘I Support My Friends’ intervention and engagement booster designed to enhance attendance and programme completion through incentives. The study will recruit 720 families and involve 64 clusters in North Macedonia and Moldova. Primary outcomes will include adolescent internalising problems and social support, family functioning and attendance during the programme. Secondary outcomes will assess broader aspects of mental health among caregivers and adolescents, as well as implementation and cost outcomes. Data will be collected at baseline and postintervention, approximately, 8 weeks later. Statistical analyses will include regression models to assess the main and interaction effects of the intervention components and cost analyses.