Mentalisation-based treatment for antisocial personality disorder in males convicted of an offence on community probation in England and Wales (Mentalization for Offending Adult Males, MOAM): a multicentre, assessorblinded, randomised controlled trial

Summary
Background
Antisocial personality disorder is a major health and social problem, but scepticism about its treatability has restricted development of the evidence base for psychological treatments. Mentalisation-based treatment (MBT) tailored for antisocial personality disorder (MBT-ASPD) can address problematic behaviours by improving the ability to understand and regulate the negative effects of thoughts and feelings. This study aimed to evaluate the clinical and cost-effectiveness of MBT-ASPD compared with probation as usual in reducing aggressive behaviours from baseline to 12 months of follow-up.
Methods
The Mentaliziation for Offending Adult Males (MOAM) trial was a multicentre, two-group, pragmatic, assessor-masked, randomised controlled superiority trial in England and Wales. Eligible participants were male, aged 21 years or older, convicted of an offence and under National Probation Service supervision at one of 13 sites, identified through the Community Personality Disorder Pathways Service, met DSM-5 criteria for antisocial personality disorder, and scored at least 15 on the Overt Aggression Scale-Modified (OAS-M). After a three-stage screening process, consenting participants were randomly allocated (1:1), stratified by site, age, probation order type, and remaining probation duration, to either MBT-ASPD plus probation as usual, or probation as usual alone. Participants in the MBT-ASPD group were offered 12 months of weekly 75-min group therapy sessions and monthly 50 min individual sessions. Probation as usual lasted up to 12 months, after which participants continued under National Probation Service supervision for the remainder of their term. Investigators and data collectors were masked to treatment allocation. The primary outcome was aggression measured by the OAS-M at 12 months after random allocation. Data were collected by a hybrid team of traditional researchers and researchers with lived experience of the criminal justice system. The primary analysis was conducted in the intention-to-treat population using a linear mixed-effects model, adjusted for baseline at each follow-up timepoint (months 3, 6, 9, 12, 15, 18, 21, and 24). This trial is registered with ISRCTN (ISRCTN 32309003), and all pre-planned follow-ups are complete.
Findings
Between Jan 2, 2016, and Aug 31, 2018, 1946 individuals were referred to the study; after the screening process, 313 participants were randomly allocated (156 [50%] to probation as usual and 157 [50%] to MBT-ASPD plus probation as usual). Participants had a mean age of 34·2 years (SD 9·3); the majority of participants (247 [79%]) identified as White British, Irish, or White Other; followed by Black British (Caribbean, African, or Other; 30 [10%]) or Mixed (29 [9%]). At 12 months after random allocation, mean OAS-M scores were significantly higher in the probation as usual group (mean score 186 [SD 153]) than in the MBT-ASPD group (90 [126]), with an adjusted mean difference between groups of –73·5 (95% CI –113·7 to –33·2); p<0·0001, with a medium-to-large effect size of 0·74. During the trial, seven participants died, and one presumed death occurred, all in the probation as usual group after random allocation, with none of the deaths deemed related to trial procedures.
Interpretation
MBT-ASPD holds promise as an effective intervention for individuals with antisocial personality disorder within a forensic population. Future research should explore these findings’ generalisability and the sustainability of treatment gains.