Non-suicidal self-injury (NSSI) is highly prevalent among individuals with borderline personality disorder (BPD) and a robust predictor of future suicide attempts and death. Access to comprehensive treatments such as dialectical behaviour therapy remains limited. This exploratory study evaluated the feasibility and preliminary outcomes of a brief, group-based mindfulness-based cognitive therapy program tailored to reduce NSSI (MBCT-NSSI) and improve associated psychological processes. Using a nonrandomised within-subject pre–post design with a waiting-period comparison, assessments were conducted at baseline (T1; n = 120), pre-intervention (T2; n = 72), and post-intervention (T3; n = 50). Outpatients with BPD and recent NSSI participated in a 9-week MBCT-NSSI group programme; key exclusions were acute suicide risk, psychosis, mania, and severe substance use. Primary outcomes were NSSI frequency and mindfulness. Secondary outcomes included self-compassion, self-esteem, impulsivity, depression, dissociation, and emotion regulation. Within-subject changes were analysed via linear mixed modelling and Wilcoxon signed-rank tests. Binary logistic regression identified predictors of dropout among eligible participants. No blinding or randomisation procedures were applied. Among completers (N = 50), primary outcomes showed a significant reduction in NSSI frequency and an increase in mindfulness. Improvements were also observed across several secondary outcomes, including depressive symptoms, impulsivity, and emotion regulation. For mindfulness and secondary self-report outcomes, changes were observed between T2 and T3 but not during the waiting-list period. For NSSI, which was evaluated only at T1 and T3, findings should be interpreted as preliminary signal detection. Dissociative symptoms showed a non-significant trend toward improvement. Dropout among eligible patients was associated with higher impulsivity, maladaptive regulation, and, unexpectedly, higher self-compassion, whereas fewer comorbid diagnoses predicted lower treatment retention. MBCT-NSSI may be a feasible and potentially beneficial adjunctive intervention for individuals with BPD who engage in NSSI, with improvements in emotion regulation and preliminary signals of reduced self-harm frequency. These findings support further investigation through controlled trials and longer follow-up. Not applicable. The study had a within-subject pre–post design without a control condition, and therefore does not meet the ICMJE definition of a clinical trial. De-identified data are openly available via the Open Science Framework (OSF): https://doi.org/10.17605/OSF.IO/ZUR84.
Kresznerits et al. (2026) studied this question.