RCT of 219 Adolescents Finds Therapist-Guided Internet Behavioral Activation Outperforms Usual Care for Depression at Lower Cost

The three-arm RCT assigned 219 participants to 10 weeks of therapist-guided internet behavioral activation, self-guided internet behavioral activation, or usual care in child and adolescent mental health services. Clinician assessors masked to allocation measured depressive symptoms at three-month follow-up; both internet arms cost less than usual care, with the self-guided version cheapest. Predefined primary analysis favored therapist support over usual care, yet an alternative model rendered the difference non-significant, illustrating sensitivity to analytic choices. This pattern echoes earlier digital CBT trials in adult primary care where guidance improves adherence but effect sizes shrink when implementation varies. Cost-effectiveness data fill a gap left by most adolescent depression studies that omit economic endpoints. Self-guided formats may expand reach where therapist supply is constrained, yet heterogeneity in response demands better stratification. Long-term follow-up, still pending, will test durability beyond three months. Next studies should embed active usual-care comparators with fidelity checks and pre-specify analytic hierarchies to reduce post-hoc ambiguity.