Multilevel associations between skills use, engagement, and treatment outcome in self-guided internet-delivered dialectical behavior therapy for substance use disorders.

Internet-delivered dialectical behavior therapy (iDBT) represents a scalable and accessible treatment approach for individuals with substance use disorders (SUDs), yet little is known about the mechanisms of change and the role of engagement in this format. This study examined within- and between-person associations between changes in skills-based constructs (mindfulness, DBT skills use, emotion dysregulation) and two treatment outcomes (SUD severity and functional disability) across a 12-week self-guided iDBT program. The moderating role of treatment engagement was also evaluated. 72 participants with past year SUDs were randomized to immediate or delayed iDBT and completed assessments at baseline and weeks 4, 8, and 12. Multilevel models were used to assess within- and between-person associations between skills and outcomes over time. Several indices of engagement were used including treatment acceptability, usability, and hours/days spent on iDBT. Within-person increases in emotion dysregulation were associated with higher SUD severity and disability, over and above respective between-person effects. DBT skills and mindfulness were not significantly associated with outcomes after correction for multiple tests, though the latter produced a small-medium effect size at the between-persons level. There were no significant moderation effects of treatment outcomes after correction for multiple tests, but several produced small-medium effect sizes. These preliminary findings support the role of emotion dysregulation as a key correlate of treatment response and promote further research within an iDBT context. Future work should refine measurement of DBT skill acquisition and investigate longer-term functional impacts of digital DBT interventions.