Internet-delivered unguided psychodynamic vs. cognitive behavior therapy for anxiety and depression symptoms: A large, full factorial randomized controlled trial on treatment length and peer support.

OBJECTIVE: Depressive and anxiety disorders are highly comorbid and widely prevalent, yet a significant treatment gap remains. Scalable, unguided transdiagnostic internet interventions may increase access to care. This study evaluated the efficacy of two distinct unguided transdiagnostic treatments, internet-delivered cognitive behavioral therapy based on Unified Protocol (UP) and internet-delivered affect-focused psychodynamic therapy (IPDT). Furthermore the study examined the impact of treatment duration and assessed the value of peer support.

METHOD: In a 3 × 2 × 2 factorial design, adults in Sweden with self-reported symptoms of depression and/or anxiety (N = 2477) were randomized to one of three conditions: UP, IPDT, or a waitlist control. Participants were also independently randomized to a treatment duration of 8 or 16 weeks, and to receiving access to a peer discussion forum or no forum access. The primary outcomes were symptom severity of depression and anxiety, while quality of life served as a secondary outcome. Data were analyzed using linear mixed models.

RESULTS: Overall, adherence was low, with participants completing fewer than half of the treatment modules on average and high attrition on measurements. At posttreatment, both UP and IPDT resulted in significant reductions in depressive and anxiety symptoms compared to the waitlist control, with small to moderate between-group effect sizes (d = 0.38-0.65). Results remained stable during a 24-month follow-up. Both interventions also led to greater improvements in quality of life than the control condition. Head-to-head comparisons revealed no significant differences in primary outcomes between UP and IPDT. Furthermore, extending the treatment duration from 8 to 16 weeks yielded no significant differences in symptom reduction. Access to a peer discussion forum provided no additional benefit.

CONCLUSIONS: Unguided transdiagnostic internet interventions can effectively reduce symptoms of depression and anxiety and improve quality of life. Since the 16-week duration provided no added value over the 8-week format, the shorter duration appears sufficient for unguided delivery. However, the low adherence rates suggest that unguided self-help may not be suitable for everyone. The substantial attrition, particularly at follow-up, limits the interpretability of long-term outcomes and highlights the need for strategies to improve engagement in unguided formats.

TRIAL REGISTRATION: ClinicalTrials.govNCT05016843.