Together and beyond: A systematic review on characteristics and efficacy of transdiagnostic psychotherapeutic group-based interventions for children and adolescents

Transdiagnostic group interventions address the limitations of youth mental health care services, including the disorder-specific nature of existing treatments and the limited capacity of individual psychotherapies. This review synthesizes the 1) characteristics, applications, parental involvement, patient and public involvement (PPI), and 2) data on efficacy, adherence, safety and treatment satisfaction evidence of transdiagnostic group interventions for children and adolescents. Following PRISMA guidelines, a preregistered systematic literature search identified 6845 publications on transdiagnostic in-person group-based interventions for children and adolescents (mean age ≤ 18 years). Two reviewers independently screened for inclusion, extracted data, and assessed risk of bias using the RoB-2 and ROBINS-I tool. The review examined 80 studies encompassing 4152 participants (M_{age =} 12.81 years), mostly conducted in high-income countries. Cognitive behavioural therapy was the most commonly used approach (κ = 59), with the core components mindfulness, emotion regulation, and cognitive restructuring. Interventions averaged 11 sessions and 52 % involved parents. 22 studies targeted anxiety and depression jointly with positive pre-post effects. Significant reductions in symptom severity were also reported for other disorders, though outcome measures highly varied and group comparisons with active control conditions or treatment-as-usual were often non-significant. Few studies examined disorder-unspecific outcomes like psychosocial functioning, quality of life, or reported remission rates, treatment satisfaction or applied a PPI framework. While a large number of different transdiagnostic group interventions for youth have been developed and evaluated, the lack of rigorous reporting and high risk of bias highlight the need for better-quality research to strengthen evidence and improve clinical implementation.