Mentalization-Based Treatment for Antisocial Personality Disorder: Evaluating the Implementation of a Randomized Controlled Trial in the UK Criminal Justice System

Randomized controlled trials (RCTs) are the gold standard for evaluating interventions, yet their use in criminal justice settings remains limited and challenging. This qualitative study examined barriers encountered during a multi-site RCT of mentalization-based treatment for men with antisocial personality disorder (ASPD) under probation community supervision in the United Kingdom. Sixteen focus groups were conducted with mentalization-based treatment therapists, offender managers, psychologists, and research staff across 13 sites. Thematic analysis identified five primary challenges: Staff emotional burden, Participant attrition, Systemic constraints within the justice system, Trial design challenges, and Intervention-specific implementation problems. Staff emotional burden emerged as a substantial and under-recognized barrier, associated with systemic instability, professional isolation, and the demands of sustained clinical work with resistant participants. In response, the trial introduced adaptive strategies intended to mitigate these barriers, including strengthened leadership structures, enhanced supervision, improved engagement with probation services, involvement of peer researchers to support trust and participation, and increased procedural flexibility to accommodate participants’ circumstances. These findings underscore the value of embedding qualitative evaluation within RCTs to support timely, targeted adaptations that enhance feasibility, staff well-being, and retention. Despite the inherent complexity of conducting trials in criminal justice contexts, responsive and reflexive trial design can support ethical and rigorous evaluation of psychological interventions for high-risk populations.