Evaluating a brief MBCT programme for non-suicidal self-injury in individuals with BPD: A quasi-experimental, nonrandomised pre–post design pilot study

Background Non-suicidal self-injury (NSSI) is highly prevalent among individuals with borderline personality disorder (BPD) and is one of the most robust predictors of future suicide attempts and suicide deaths. Access to comprehensive treatments such as dialectical behaviour therapy remains limited. Methods 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 pre–post design with a within-subject waitlist control comparator, assessments were conducted at three time points: 8–12 weeks pre-intervention (T1) (n = 120), immediately pre-intervention (T2) (n = 72), and post-intervention (T3) (n = 50). Outpatients diagnosed with BPD and recent NSSI were recruited from psychiatric clinics to participate in a 9-week MBCT-NSSI group programme. Exclusion criteria included current psychosis, manic episodes, severe substance use, and acute suicide risk. 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. Results Participants who completed the MBCT-NSSI intervention (N = 50) presented significant reductions in NSSI frequency, depressive symptoms, hopelessness, impulsivity, and maladaptive emotion regulation, alongside improvements in mindfulness, self-compassion, and self-esteem. These changes were observed primarily during the intervention phase and not during the waiting-list period, suggesting treatment-specific effects. Dissociative symptoms showed a non-significant trend toward improvement. Dropout among eligible patients (N = 120) was associated with higher impulsivity, maladaptive regulation, and, unexpectedly, higher self-compassion, whereas fewer comorbid diagnoses predicted lower treatment retention. Conclusions MBCT-NSSI may be a feasible and effective adjunctive intervention for individuals with BPD who engage in NSSI, improving emotion regulation and reducing self-harm frequency. These findings support further investigations via controlled trials and longer follow-up periods. Trial registration: Not applicable. The study was a nonrandomized, quasi-experimental pre–post design without a control condition, and therefore does not meet the ICMJE definition of a clinical trial. The study was retrospectively registered on the Open Science Framework (OSF) at https://doi.org/10.17605/OSF.IO/ZUR84.