Treating a common behavioural disorder in convicted criminals could dramatically reduce the risk of them re-offending, new research suggests.
One of the biggest studies of its kind has found that people diagnosed with attention deficit hyperactivity disorder (ADHD) are at least 30% less likely to commit crime if they are given medication.
The researchers now say that if prisoners suffering from ADHD were identified and treated, the impact on the criminal justice system could be significant.
Previous studies have suggested at least one in 10 inmates has the condition, but few are formally diagnosed at present.
Researcher Dr Seena Fazel, of Oxford University, said: "There quite a lot of people with ADHD that end up in the prison system, so preventing them getting stuck in the system and repeat offending is important."
A diagnosis of ADHD is usually made in childhood as a result of disruptive classroom behaviour.
Around 5% of children are diagnosed with the condition and many are treated with drugs such as Ritalin.
Many children stop treatment in adolescence, yet a third will continue to suffer significant symptoms in adulthood, including inattention, impulsiveness and anger outbursts.
The scientists tracked more than 25,000 people in Sweden with ADHD.
Over a period of four years 37% of the men and 15% of the women were convicted of a crime, compared to the rate in the general population of 9% and 2% respectively.
Drug treatment for ADHD was associated with a 32% drop in offences by men and 41% in those by women, according to results published in the New England Journal of Medicine.
Professor Philip Asherson of the Institute of Psychiatry told Sky News that medication could save huge sums of public money.
"It might cost £1,000 a year to be on a drug treatment," he said.
"On the other hand going to court once costs more than that. Being in prison costs very much more than that."
He said medication was also more likely to enable people with ADHD to find a job.
Anthony Reynolds' life spiralled out of control when he stopped taking medication for ADHD at the age of 16. He says doctors must recognise symptoms in adults.
"I became a social recluse," he said.
"I started to abuse narcotics and drink heavily. I would hide away from the world. I didn't want to deal with the pressures coming from my behaviours."
A Department of Health Spokesperson said: "This Government is committed to supporting the health needs of those in custody and to breaking the cycle of re-offending.
"We are developing a network of liaison and diversion services which will help reduce re-offending by ensuring that when people arrive in a court or police station, they get quick access to any healthcare treatment that they need."