["Journal of Child Psychology and Psychiatry, EarlyView. ", "\n\nBackground\nThere are no evaluated family‐based mental health and psychosocial support (MHPSS) interventions for adolescents in Southwest Asia (known as the Middle East), and few whole‐family interventions in low‐ and middle‐income countries, despite consistent evidence for the impact of family support on mental health and well‐being. This study aims to evaluate the effectiveness of a brief family systemic mental health intervention, deliverable by non‐specialists in mental health.\n\n\nMethods\nWe conducted an assessor‐blind type I hybrid effectiveness‐implementation multi‐site randomized controlled trial comparing the locally developed family intervention to a waitlist control group for randomly allocated families residing in North Lebanon and Beqa’a governorates. Eligible families presented with medium‐to‐high risk for child protection concerns (abuse, neglect, child labor, early marriage) and had at least one adolescent aged 12–17 who demonstrated psychological distress. Outcomes at the family, caregiver, and adolescent level were measured pre‐ and post‐intervention, and at 3‐month follow‐up.\n\n\nResults\nIntent‐to‐treat analyses found a significant between‐group effect of the intervention on adolescent‐reported family functioning, caregiver mental health, and parenting. No change was found for adolescent psychological distress. Further analyses found effects on adolescent well‐being for those who completed the intervention, and that father attendance was associated with better outcomes for adolescent well‐being in the intervention group. No other significant moderators were found. At the 3‐month follow‐up for the intervention condition, family functioning and caregiver well‐being significantly dropped from endline.\n\n\nConclusions\nThe study demonstrates mixed results for a non‐specialist‐delivered family‐systemic intervention developed in the context of humanitarian crises in Lebanon. While the intervention did not result in benefits in adolescent‐reported symptoms of psychological distress, the intervention group did show greater improvements than the control group on a number of other outcomes, showing the potential impact of working with the wider family system to support adolescents in humanitarian settings.\n\n"]