Internet-delivered cognitive behavioral therapy for adolescents with excessive worry: a randomized controlled trial with mediation analysis.

Excessive worry is common during adolescence and across psychiatric disorders. This study investigates whether: (1) internet-delivered cognitive behavioral therapy (ICBT) focused on exposure to uncertainty is effective in reducing excessive worry; (2) improvements in worry are associated with reductions in other psychiatric symptoms; and (3) changes in intolerance of uncertainty (IU) mediate worry outcomes. Adolescents (N = 62; aged 13-17 years) with excessive worry (≥30 total score on Penn State Worry Questionnaire for Children) were randomly allocated to 8 weeks of ICBT (n = 31) or a waitlist for ICBT (Waitlist, n = 31). Self-reported worry (primary outcome) was measured weekly for 12 weeks and controlled effects assessed at week 12 post-baseline. IU and a comparator mediator (depression) were measured every other week for 12 weeks during the treatment/waitlist phase. ICBT yielded significantly large reductions in worry compared to Waitlist (bootstrapped d = 0.59). Worry reductions mediated improvements in anxiety and depression symptoms. Changes in depression, but not IU, mediated worry outcomes. A brief course of worry-focused ICBT yielded moderate reductions in worry that was associated with improvements in anxiety and depression. Contrary to expectation, changes in IU did not explain worry reductions in this uncertainty- focused treatment. Further studies are needed to identify potential change mechanisms.