Supplementary Material for: Short-term versus long-term mentalization-based therapy for borderline personality disorder: a randomized clinical trial (MBT-RCT)

Introduction Borderline personality disorder (BPD) is a prevalent psychiatric disorder. Mentalization-based therapy (MBT) is an evidence-based intervention, and several countries offer long-term treatments for BPD, which is resource demanding. No previous trial has compared short-term with long-term MBT. Objective To assess the efficacy and safety of short-term versus long-term MBT for outpatients with BPD. Methods Adult outpatients (≥18 years) with subthreshold or diagnosed BPD were randomly assigned (1:1) to short-term MBT (5 months) or long-term MBT (14 months) using a web-based system. The primary outcome was BPD symptoms assessed with the Zanarini Rating Scale for Borderline Personality Disorder. Secondary outcomes were functional impairment, quality of life, global functioning, and severe self-harm. All outcomes were primarily assessed at 16 months after randomization. This trial was prospectively registered at ClinicalTrials.gov, NCT03677037. Results Between October 4, 2018, and December 3, 2020, we randomly assigned 166 participants to short-term MBT (n=84) or long-term MBT (n=82). Regression analyses showed no evidence of a difference when assessing BPD symptoms (MD 0.99; 95% CI -1.06 to 3.03; p = 0.341), level of functioning (MD 1.44; 95% CI -1.43 to 4.32; p = 0.321), quality of life (MD -0.91; 95% CI -4.62 to 2.79; p = 0.626), global functioning (MD -2.25; 95% CI -6.70 to 2.20; p = 0.318), or severe self-harm (RR 1.37; 95% CI 0.70 to 2.84; p = 0.335). More participants in the long-term MBT group had a serious adverse event compared with short-term MBT (RR 1.63; 95% CI 0.94 to 3.07; p = 0.088) primarily driven by a difference in psychiatric hospitalizations (RR 2.03; 95% CI 0.99 to 5.09; p = 0.056). Conclusion Long-term MBT did not lead to lower levels of BPD symptoms, nor did it influence any of the secondary outcomes compared with short-term MBT.