Common psychiatric disorders—including bipolar disorder and drug abuse—have been linked to ex-prisoners committing violent crimes after release, according to new research published in The Lancet Psychiatry Journal.

“One in seven prisoners have a psychotic illness or major depression and around one in five enter prison with clinically significant substance abuse disorders. As these disorders are common and mostly treatable, better screening and mental health services before and after release are essential to prevent future violence and improve both public health and safety,” said Seena Fazel, lead author and professor of forensic psychiatry at the University of Oxford, in a press release.

A team of researchers from Sweden and the UK utilized national registries to examine common psychiatric disorders and violent convictions in prisoners released between the first of January in 2000 and December 31, 2009. Researchers also compared the rates of violent reoffenses with prisoners with similar characteristics, but who did not have psychiatric disorders. The study involved almost 48,000 ex-prisoners, and found that male prisoners with a psychiatric disorder were 63 percent more likely to commit a violent offence after release than other prisoners, and female prisoners with a disorder were twice as likely.

All types of psychiatric diagnoses were associated with an increased rate of violent reoffending, but researchers found higher rates of reoffending for prisoners with a history of alcohol or drug abuse, personality disorder, attention deficit disorder, schizophrenia, and bipolar disorder.

The researchers caution that further study is needed before psychiatric disorders can be casually linked to violent reoffending, but that the study is an important first step.“Because the number of prisoners with psychiatric disorders is large, our findings suggest that better mental health care in prison and stronger links with community health services could improve both prisoners’ quality of life and go a long way toward counteracting the cycle of violent reoffending,” said Fazel in a university press release. Fazel added that better treatment could lead to significant reductions in the number of violent crimes committed every year, and that the research highlights the importance of treating alcohol and drug misuse.

The study authors called for national programs addressing violence prevention to be implemented in prison health programs.

Source: Fazel S, Chang Z, Lichtenstein P, Larsson H.“Substance use disorders, psychiatric disorders, and mortality after release from prison: a nationwide longitudinal cohort study.” The Lancet. 2015.