Criminal behaviour is lower in people with attention-deficit hyperactivity disorder (ADHD) when they are on medication for the condition, a Swedish study has found.
Oxford University psychiatrist and Wellcome Trust Senior Research Fellow Dr Seena Fazel, a co-author on the study, says: 'Our findings suggest a consistent, reasonably strong effect on criminality.
'It has to be weighed up against the other advantages and possible side-effects of the drugs, but it does add to the bigger picture,' says Dr Fazel. 'Here we have a medication that is prescribed widely with a clear benefit for one important outcome.'
The research used extensive registries that are available in Sweden on ADHD diagnoses, prescriptions and criminal convictions. The study included four years of data from 2006 through 2009 for over 25,000 adults with ADHD, and is published in the New England Journal of Medicine (NEJM).
Criminality was reduced by over 30% in people with ADHD when they were taking drugs for the condition compared to periods when they were off medication.
he study found the same pattern in men and women, and it applied as much to petty crime as it did to serious or violent crime.
ADHD tends to be first diagnosed in childhood and involves a number of symptoms that have a major impact on family and school life. These include overactivity, impulsivity, lack of attention and an inability to concentrate. It is more than just being a difficult child or a busy toddler.
Estimates suggest that around 4 to 5% of schoolchildren and possibly half as many adults have ADHD. Research has shown that ADHD is a relatively stable condition and many of those who are diagnosed as children also meet the criteria for ADHD as adults.
While it is known that people with ADHD are more likely to commit crimes than the general population, it has remained uncertain whether medication for the condition such as Ritalin can have an effect on this.
'The study was driven largely because of the large amount of prescribing of medication for ADHD and the relatively small amount of evidence on the long-term effects of the drugs,' says Dr Fazel. 'Because ADHD drugs are so widely used, this is an important question. Up to 10% of boys in the USA are getting this diagnosis, and it’s about 5% worldwide.
'We need to understand what happens to long-term mental health, and whether these drugs continue to have an effect on symptoms, but also look at other outcomes like school performance, employment prospects and so on.'
The strength of the study lies in the comparison between crime rates for individuals when they were on medication and when they were not. The researchers essentially were able to use the same person as their own control.
This approach avoids the problem of other studies comparing groups of people on medication with those who are not, when the two groups aren't necessarily similar. Those being prescribed drugs may be on them precisely because they are more at risk, for example.
'We have shown that ADHD medication very probably reduces the risk of crime,' says Professor Henrik Larsson of the Karolinska Institutet in Sweden, the senior author on the study. 'However, we need to point out that most medical treatments can have adverse side effects, so risks must be weighed up against benefits and the individual patient's entire life situation taken into consideration before medications are prescribed.'
Professor Paul Lichtenstein, who led the study at the Karolinska Institutet, adds: 'Of course the potential pros and cons of each prescription have to be evaluated. What we're saying is that this probable reduction in the risk of crime must also be taken into account.'
Dr Fazel adds: 'This is part of a wider trend for psychiatrists to think about the wider implications of treatment decisions. Our role as doctors is not just limited to the patient but can involve public health and safety considerations as well. But the primary thing is that it's in the best interests of individual patients – obviously so. Their health is improved if they’re not getting into trouble. Health has these broader elements to it. It’s not just a matter of improving an individual's symptoms, but how well they do in life more generally, including at school, in employment and without engaging in antisocial behaviours and crime.'
The study was funded by the Swedish Research Council, the Swedish Council for Working Life and Social Research, the Swedish Prison and Probation Service, the National Institute of Child Health and Human Development, and the Wellcome Trust.