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The study, published in and funded by the National Institute for Health & Care Research (NIHR), investigated whether aggression and antisocial behaviours could be improved by a modified form of mentalisation-based treatment (MBT). 

Trialling the treatment, which has been found to substantially reduce rates of violence and aggression in male offenders who have the condition, was supported by the North Wales Organisation for Randomised Trials in Health (& Social Care) (NWORTH) - a UKCRC accredited clinical trials unit based at 91�����. 

Dr Zoe Hoare, Director and Principal Statistician at NWORTH, said, “NWORTH played a key role in this research by managing and ensuring the quality of the data from different sources. 

“The team was also able to use a specialised system to randomly assign participants to the treatment or control group. This system employed a specially designed randomisation algorithm that is unique to NWORTH. Our work helped ensure that the study was conducted to the highest standards.  

“NWORTH is proud to be able to support evaluations of complex interventions within settings such as prisons. We are able to offer the systems and expertise to be ensure important studies like these are delivered to the highest quality.” 

Mentalisation-based treatment is a type of therapy that helps people to understand their own thoughts and feelings, as well as those of others.  

The new treatment, known as MBT-ASPD, was designed by a team of UCL-led researchers. It aimed to enhance the ability of male offenders with ASPD to recognise and reflect on both their own and others' thoughts and feelings, helping to improve interpersonal interactions and decision-making. 

Antisocial Personality Disorder is a mental health condition characterised by a persistent pattern of disregarding or violating the rights of others. Symptoms include deceitfulness, impulsivity, aggression, recklessness and a lack of remorse. It frequently involves criminality. 

For the largest study of its kind, 157 male offenders on probation with ASPD in England and Wales received a 12-month course of MBT-ASPD alongside standard probation services. A control group of 156 participants received probation services without MBT-ASPD.  

The treatment involved weekly 75-minute group therapy sessions led by two trained MBT clinicians, often supported by an expert by experience. The group enabled participants to explore social interactions including their personal values, observe how others thought about issues that concerned them, how their actions were seen by others and how their perceptions of themselves corresponded to others’ perceptions of them.  

Participants also received monthly 50-minute individual therapy sessions. These sessions focused on developing mentalising skills (such as self-awareness, empathy for others, perspective taking and reflective thinking), particularly in situations of interpersonal conflict. 

The results revealed that men who received MBT-ASPD had aggression levels approximately 50% lower than those in the standard probation services.   

While both groups showed a decrease in ASPD symptoms, the MBT-ASPD group showed a significantly greater decrease of 63% in the number of symptoms at the 12 months follow-up.  

Additionally, men in the MBT-ASPD group committed 46% fewer offences than those in the standard probation group over a three-year follow-up period.  

Chief Investigator Professor Peter Fonagy (UCL Psychology & Language Sciences) emphasised the broader impact of the findings: “Given the enormous personal and societal costs of antisocial personality disorder—including higher risk-taking, poorer health outcomes, reduced employment, and an estimated £16.7 billion annual economic burden in the UK—this study represents a major breakthrough. 

“Antisocial personality disorder has historically been difficult to treat, but our findings demonstrate that a psychological intervention requiring relatively limited therapist training can meaningfully improve outcomes for individuals with this condition while also reducing their impact on society.” 

Despite previous mixed results from other psychological treatments such as Cognitive Behavioural Therapy (CBT), MBT-ASPD offers a promising new approach for male offenders. The study provides some of the strongest evidence to date that structured therapy can be effective in reducing aggression and criminal behaviours among individuals with ASPD. 

The study was carried out in collaboration with researchers at Anna Freud, Newcastle University, King’s College London, Royal Holloway, the National Probation Service London Division, University of Prince Edward Island, 91�����, University of Nottingham and Imperial College London. 

Study limitations 

While the results are promising, the study had some limitations. The design made it challenging to isolate the specific effects of MBT-ASPD from the additional attention participants received.  

Data collection issues and missing data—exacerbated by COVID-19-related delays—may also have impacted the findings.  

Furthermore, since the study focused on male offenders aged 21 and older under probation supervision, the results may not be directly generalisable to other populations, such as younger offenders or those outside the probation system.