Supplementary Material for: Effectiveness and Cost-Effectiveness of Dialectical Behaviour Therapy for Self-Harming Patients with Personality Disorder: A Pragmatic Randomised Controlled Trial

Background: A primary goal of dialectical behaviour therapy (DBT) is to reduce self-harm, but findings from empirical studies are inconclusive. The aim of this study was to assess the effectiveness and cost-effectiveness of DBT in reducing self-harm in patients with personality disorder. Methods: Participants with a personality disorder and at least 5 days of self-harm in the previous year were randomised to receive 12 months of either DBT or treatment as usual (TAU). The primary outcome was the frequency of days with self-harm; secondary outcomes included borderline personality disorder symptoms, general psychiatric symptoms, subjective quality of life, and costs of care. Results: Forty patients each were randomised to DBT and TAU. In an intention-to-treat analysis, there was a statistically significant treatment by time interaction for self-harm (incidence rate ratio 0.91, 95% CI 0.89–0.92, p Conclusions: DBT can be effective in reducing self-harm in patients with personality disorder, possibly incurring higher total treatment costs. The effect is stronger in those who complete treatment. Future research should explore how to improve treatment adherence.