A breakthrough for treating antisocial personality disorder

Antisocial personality disorder (ASPD) has long been considered one of the most challenging mental health conditions to treat. It is characterised by persistent patterns of aggression, recklessness, and disregard for others, and is linked to violent offending and high rates of reoffending. Now, thanks to new mentalisation-based treatment (MBT) services developed by Dr Jessica Yakeley at the Portman Clinic (an internationally renowned thought leader in the field of forensic psychotherapy), that may be changing.

Groundbreaking research led by Professor Peter Fonagy at University College London, published in The Lancet Psychiatry offers compelling evidence that MBT adapted specifically for ASPD, can make a real difference. The Mentalisation for Offending Adult Males (MOAM) trial (a large, multi-site, randomised clinical trial with blinded assessments), evaluated whether MBT could reduce aggression among male offenders on probation in England and Wales. The results were striking: MBT significantly reduced aggression compared to probation as usual, with benefits persisting beyond the treatment period. This is a major step forward both for rehabilitation and public safety.

What is mentalisation-based treatment?

Mentalisation-based treatment (MBT) is a psychological therapy grounded in attachment theory. It focuses on improving ‘mentalising’ – the ability to understand and reflect on one’s own and others’ thoughts, feelings, and intentions. People with ASPD often struggle with mentalising, leading to impulsive aggression and difficulty recognising the impact of their actions on others. MBT aims to strengthen these skills, fostering empathy, emotional regulation, and more constructive interpersonal behaviour.

In the MOAM trial, participants in the MBT group received 12 months of weekly group sessions and monthly individual therapy, alongside standard probation supervision. The therapy encouraged participants to explore the mental states underlying their behaviour, particularly in conflict situations, and to develop strategies for managing emotions and impulses.

The study design

The trial recruited 313 men aged 21 and over, all convicted of an offence and under National Probation Service (NPS) supervision. Each participant had a confirmed diagnosis of antisocial personality disorder and scored above the aggression threshold on a standard measure, the Overt Aggression Scale-Modified (OAS-M). They were then randomly assigned to either mentalisation-based therapy plus probation or probation alone.

The primary outcome was aggression, measured at 12 months using the OAS-M. Secondary outcomes included violence, anger, hostility, mental health symptoms, and reoffending rates over three years. Importantly, the study also examined whether improvements in mentalising mediated reductions in aggression: a key test of MBT’s theoretical foundations.

A notable innovation was the involvement in the trial of peer researchers and experts by experience with lived experience of the criminal justice system, to enhance data collection, recruitment and retention of participants in the trial as they were more likely to gain the offenders trust than professionals.

Key findings

The results speak volumes. After 12 months, men who received mentalisation-based therapy were far less aggressive than those on probation alone. Their scores dropped by more than 50% (an adjusted mean difference of 73.5 points on the OAS-M), showing a strong and meaningful effect. The improvement lasted for six months after treatment ended, though it started to fade by two years.

Secondary outcomes reinforced the picture. MBT participants showed significant reductions in violent behaviour at 12 months, improved negotiation skills in intimate partner conflict by 18 months, and lower hostility scores. They also demonstrated better mentalising, with reduced uncertainty about mental states: a change that fully mediated the impact on aggression. In other words, MBT worked by improving the capacity it targets.

Perhaps most encouragingly, MBT participants were less likely to meet diagnostic criteria for ASPD at follow-up, suggesting the therapy may contribute to remission. Official records revealed a significant reduction in major offences by the third year after randomisation, with rates about 58% lower (an incidence rate ratio of 0.42) than for those on probation as usual. Attendance mattered: those who attended at least half of their MBT sessions had the greatest improvements in aggression and the lowest reoffending rates.

Why this matters

For decades, scepticism about whether ASPD could be treated has limited progress in developing effective psychological interventions. These findings challenge the long-held belief that ASPD is untreatable. They show that a structured, relational intervention can reduce aggression and even criminal behaviour in a population often considered beyond the reach of therapy. Forensic services have historically relied on punitive measures and risk management, with limited success in reducing reoffending. MBT offers a rehabilitative alternative grounded in psychological science.

The implications are profound. If replicated and scaled, MBT could transform probation services and offender rehabilitation programmes. By addressing the root causes of aggression – mentalising deficits – rather than simply managing risk, MBT has the potential to break cycles of violence and improve public safety. It could also deliver economic benefits by reducing prison recalls and long-term criminal justice costs.

A step change in criminal justice interventions

The MOAM trial is not just a clinical success; it is a methodological milestone. It demonstrates that rigorous randomised controlled trials are possible in probation settings, even with populations traditionally seen as hard to engage.

Future research should explore MBT’s applicability to broader populations, including those involved in domestic abuse, a domain where existing interventions have largely failed. Studies should also examine variations in treatment intensity and duration and assess the sustainability of gains over the long-term. The trial’s economic evaluation, due to be reported separately, will shed light on cost-effectiveness, a critical consideration for policy and commissioning.

Conclusion

The MOAM trial marks a turning point in the treatment of antisocial personality disorder. Mentalisation-based therapy, delivered alongside probation, significantly reduces aggression and shows promise in reducing reoffending. It offers hope for individuals, families, and communities affected by violence, and a new direction for criminal justice policy. For too long, ASPD has been seen as a lost cause. This research proves that change is possible and that understanding minds can change lives.

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