A large study suggests that people with serious attention deficit hyperactivity disorder are less likely to commit crimes when taking medication.
The study, published in The New England Journal of Medicine, examined records of 25,000 people in Sweden to see if those with ADHD had fewer criminal convictions when taking medication than when they were not.
Of 8,000 people whose medication use fluctuated over a three-year period, men were 32 per cent less likely and women were 41 per cent less likely to have criminal convictions while on medication. Patients were primarily young adults, many with a history of being admitted to hospital. Crimes included assault, drug offences and homicide as well as less serious crimes. Medication varied, but many took stimulants like Ritalin.
"The study adds a lot," said Dr Gabrielle Carlson, director of child and adolescent psychiatry at Stony Brook University medical school, who was not involved in the study. "Cutting the crime rate, that's not trivial. Maybe it will get some help for people in jail. It gives people who were on the fence maybe a little more confidence in this treatment."
Studies suggest that people with ADHD are more likely to commit crimes. And while people, especially boys, are often prescribed medication as children, they often resist taking it as teenagers. Studies have not shown that medication has long-term effects on symptoms.
Dr Paul Lichtenstein, a study author and a professor at Karolinska Institute, cautioned against concluding that everyone with ADHD should be continuously medicated.
"There are pros and cons to medication," he said. But "in young adults, the age where criminality is most common, you should consider medication because it is more harmful for these people to be involved in criminal activities. Also for prisoners and people who have left prison."
Among psychiatric experts, when, and sometimes whether, to prescribe ADHD medication is still debated. Drugs do not work for everyone, and side effects can include jittery feelings and suppressed appetite and growth.
William Pelham, director of the Centre for Children and Families at Florida International University, said non-drug therapies like behavioural modification worked as well as medication in the short run. He said that the study did not prove that medication caused less criminality, and because most subjects were seriously ill adults, the results were irrelevant for most US children.
Jason Fletcher, an associate professor at the Yale School of Public Health, said that despite some weaknesses, the study provided a "very suggestive piece of evidence" supporting the use of medication for ADHD.