Supplementary Material for: Internet-Delivered Treatment for Stress-Related Disorders: A Randomized Controlled Superiority Trial of Cognitive Behavioral Therapy versus General Health Promotion

Background: Stress-related disorders such as adjustment disorder (AD) and exhaustion disorder (ED) are associated with substantial suffering and high societal costs. Cognitive behavioral therapy (CBT) is a promising treatment for symptom reduction but has not been rigorously compared with other active treatments. This study aimed to investigate the efficacy of CBT compared to an active control treatment (General Health Promotion; GHP) treatment for individuals diagnosed with AD or ED. Methods: A total of 300 adults diagnosed with AD or ED were randomly assigned to a 12-week CBT (n=151) or GHP (n=149), both delivered as therapist-supported online treatments. Primary outcome was post-treatment scores on the 10-item Perceived Stress Scale. Secondary outcomes included several mental health symptom domains and functional impairment. All outcomes were assessed at baseline, post-treatment, and at 1-year follow-up. The trial was pre-registered on Clinicaltrials.gov (NCT04797273). Results: The CBT intervention was not superior to GHP in reducing symptoms of perceived stress and secondary symptoms. Both treatments generated large within-group effect sizes pre- to post-treatment (Cohen’s d= 1.19 and 1.06, respectively) and results were maintained to the 1-year follow-up. Diagnostic group moderated the treatment effect pre- to post-treatment and indicated that CBT was superior to GHP for individuals diagnosed with AD but not for those diagnosed with ED. Conclusions: Common factors likely play an important role in symptom reduction for individuals with stress-related disorders. A refined understanding of the conceptualization of stress-related disorders and which specific mechanisms to target in the respective patient groups is needed to improve treatment outcomes.