Treating a common behavioural disorder in convicted criminals could have a major impact on reoffending, a study has suggested.
Criminal behaviour in people diagnosed with attention deficit hyperactivity disorder (ADHD) falls by about a third when they are on medication, the research shows.
Translated to the prison population, similar treatment could have a dramatic effect, experts believe.
Around 4% of children in the UK and half as many adults are believed to suffer from the disorder, which is characterised by over-activity, impulsivity, aggression, short temper and disorganised thinking.
But a disproportionate number of people with ADHD end up being convicted of petty crimes, often related to violence and drug abuse. Studies suggest that anything from 10% to 40% of prison inmates have the disorder, but few are diagnosed or treated.
Treating ADHD-affected children with drugs such as the stimulant Ritalin is controversial because of the side effects, which can include nervous system disturbances and raised blood pressure and heart rate.
But the study authors say such drugs could have a real impact on crime, although their use would have to be carefully considered on a case-by-case basis.
The research was conducted in Sweden, where it is easy to access data on medical treatments and criminal convictions through national registries. Scientists studied the records of more than 25,000 individuals with ADHD, mostly teenagers and young adults.
They found that over a period of four years, 37% of the men and 15% of the women were convicted of crimes, compared with a rate in the general population of 9% and 2%. Drug treatment for ADHD was associated with a 32% drop in offending rates by men and 41% by women - an overall reduction of about a third.
The findings are published in the New England Journal of Medicine.