Effectiveness and mechanisms of internet-delivered transdiagnostic CBT for students with adjustment disorder: the role of cognitive inflexibility, self-compassion, and mindfulness.

Adjustment disorder (AjD) is highly prevalent among university students and is associated with significant distress and impaired academic functioning, yet evidence-based interventions remain limited. This randomized controlled trial evaluated the effectiveness and mechanisms of a six-week internet-delivered Unified Protocol (iCBT-UP) for students with AjD, compared with an active control (iPMR) and a wait-list control. A total of 181 students meeting ICD-11 criteria for AjD were randomized (2:2:1) to iCBT-UP (n = 79), iPMR (n = 63), or wait-list (n = 39). Assessments were conducted at baseline, post-treatment, and one-month follow-up. Outcomes included AjD, academic adjustment, experiential avoidance, self-compassion, and mindfulness. Daily diary assessments captured changes in self-compassion, mindfulness and psychological flexibility. Treatment effects were examined using mixed repeated-measures ANOVA and mediation analyses. Both active interventions significantly reduced AjD symptoms relative to wait-list, whereas only iCBT-UP improved academic adjustment. Reductions in experiential avoidance and increases in self-compassion mediated the effects of iCBT-UP on decreases in AjD symptoms. Self-compassion also mediated the effects of iCBT-UP on improvements in academic adjustment. Daily diary analyses showed increases in self-compassion and psychological flexibility in both active conditions. These findings support transdiagnostic CBT as an effective intervention for AjD and highlight key mechanisms of change.