Exploring the influence of loneliness and social isolation in transdiagnostic internet-delivered cognitive behavioral therapy for depression and anxiety

OBJECTIVE: Past research shows that social factors play an important role in mental health outcomes, but there is limited research on how these factors influence Internet-delivered cognitive behavior therapy (ICBT). This study investigated the prevalence of subjective (i.e., feelings of loneliness) and objective social isolation among patients receiving transdiagnostic ICBT. We explored whether social factors change over treatment and moderate treatment effectiveness and engagement. METHOD: This study used data collected in a routine ICBT clinic. Among clients with elevated depression and/or anxiety who started ICBT (n = 625), we analyzed measures of depression, anxiety, loneliness, and social engagement administered at pretreatment, various points during the treatment and 20 weeks follow-up. RESULTS: Pretreatment prevalence of frequent loneliness and social isolation was 75.7% and 54.6%, respectively. Depression and anxiety decreased over time, with large effect sizes from pretreatment to follow-up (depression d = 1.56; anxiety d = 1.63). Loneliness decreased significantly (d = 0.69), while social engagement improved moderately (d = 0.37). Higher pretreatment loneliness was associated with higher average levels of depression across the treatment period and with fewer completed treatment lessons. CONCLUSIONS: Overall, results indicate that loneliness and social isolation are prevalent among clients seeking ICBT and both decrease during transdiagnostic ICBT. More frequent loneliness during the treatment was associated with lower engagement and smaller treatment gains, while social isolation was not. These findings suggest that further research is warranted on how to address loneliness within ICBT. It also suggests that social isolation can be reduced by means of transdiagnostic ICBT. (PsycInfo Database Record (c) 2025 APA, all rights reserved).