Study finds mental health treatment for serious offenders reduces harm, costs

Prisoners convicted of serious violent offences who received a mental health intervention showed measurably lower aggression and were less likely to reoffend, according to new cost-effectiveness research led by King’s College London. The findings point to a potential way to reduce harm while easing pressure on healthcare and the criminal justice system.

The study, funded by the National Institute for Health and Care Research (NIHR), was published in PLOS One. It provides high-quality evidence on Mentalization Based Therapy (MBT) when delivered alongside probation support for men with antisocial personality disorder (ASPD) convicted of violent offences.

A randomized controlled trial was conducted across multiple UK prisons and probation services, enrolling more than 300 participants. Men were assigned at random to one of two groups: one group received MBT in addition to probation, while the comparison group received probation support alone.

Outcomes were assessed 24 months after allocation. Researchers estimated economic costs from a societal perspective, explicitly including healthcare expenditures, criminal justice system costs, and the broader impacts of offending. This approach links clinical change to measurable resource use.

Across the follow-up horizon, participants receiving MBT plus probation were associated with reduced costs and lower aggression. The analysis suggested potential cost savings of approximately £93 per person relative to current probation provision.

ASPD is defined by enduring patterns such as chronic aggression, irritability, deceitfulness, irresponsibility, and lack of remorse. While its prevalence in the general population is relatively low, rates can be markedly higher among men convicted of violent offences, and the condition is associated with persistent offending trajectories.

To capture real-world service use, the study used structured interviews and self-reported questionnaires covering access to accommodation, education, employment, and training. Importantly, clinicians and individuals with lived experience informed the research questions to ensure feasibility and robustness.

The average cost of delivering MBT was £826.30 per participant, comparable with other community-based psychological interventions. Those upfront costs were offset by savings elsewhere, particularly through reduced custodial time and lower offence-related costs. Although follow-up completion declined at 12 and 24 months—an issue common to long-term tracking—findings were consistent across analyses, supporting the intervention’s promise as a cost-effective strategy.