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Prisoners convicted of serious violent offenses were found to be less aggressive and less likely to reoffend following a mental health intervention that could save money and reduce harm to society, according to new research led by King's College London.
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The research, published in PLOS One, provides the first high-quality evidence of the cost-effectiveness of Mentalization Based Therapy (MBT) alongside probation for men convicted of violent crimes who have antisocial personality disorder (ASPD).
The randomized controlled trial ran across UK prisons and probation services and involved more than 300 prisoners. They were randomly split into two groups: one received the mental health intervention alongside probation support, while the other received probation support alone.
Costs fell alongside aggression
The researchers assessed the trial's outcomes 24 months after participants had been allocated to each group. They assessed economic costs to society, incorporating health care and criminal justice system costs, as well as the wider impact of offending. They found that the group that received the mental health intervention and probation had reduced costs and lower aggression, potentially saving approximately £93 per person compared with current probation service provision.
Antisocial personality disorder is characterized by a persistent pattern of behaviors including chronic aggression, recklessness, irritability, deceitfulness, irresponsibility and a marked lack of remorse. Although its prevalence in the general population is relatively low, rates can reach up to 50% among men convicted of violent offenses, where it is associated with more serious and persistent offending.
ASPD imposes a substantial economic burden on health and criminal justice services and, most importantly, contributes to serious harm and enduring consequences for victims while complicating the management of offenders in prison and communities. Despite this, evidence on the cost-effectiveness of pharmacological or psychological interventions remains extremely limited, constraining efforts to provide effective solutions and resources.
Barbara Barrett, professor of health economics at King's College London and lead author, said, "The importance of evidence-based solutions is especially important given the high rates of reoffending among individuals with ASPD. This intervention provides significant potential for long-term cost savings across health and criminal justice systems."
How the trial was built
The research team carried out the study through structured interviews and a self-reported questionnaire recording the use of services providing accommodation, education, employment and training. Clinicians and people with lived experience of prison and probation services helped develop research questions to ensure they were appropriate and robust.
The average cost of delivering MBT (£826.30 per participant) is comparable to that of other community-based psychological interventions, and this expenditure was offset by savings elsewhere, particularly through reduced custodial time and lower offense-related costs.
However, because of the complex challenges inherent in following this population over two years, there was a drop in data-completion rates for the study at 12 and 24 months. Despite gaps in the data, the researchers found consistent results across their analyses and concluded that the mental health intervention plus probation service support is a promising, cost-effective intervention for this population.
Dr. Elizabeth Simes, UCL, second author of the study, said, "This study is the first multisite randomized controlled trial conducted within the National Probation Service in England and Wales and is strengthened by the involvement of a hybrid research team comprising researchers with and without lived experience. The study demonstrates that a psychological intervention can improve outcomes and is cost-effective for a population that has traditionally been considered difficult to treat."
More information: Cost-effectiveness of a mentalisation-based treatment for antisocial personality disorder in males convicted of an offence on community probation in England and Wales, PLOS One (2026). DOI: 10.1371/journal.pone.0352865
Provided by King's College London
This story was originally published on Medical Xpress.
