Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder characterised by persistent inattention, impulsivity and hyperactivity. These characteristics may mean that children with ADHD are more at risk of sustaining injuries.

The most common form of treatment for ADHD is stimulant medication. This recent study investigated the effect of stimulant medication on the prevalence of injuries and emergency ward visits in children with ADHD.

Methods

Data were collected from national databases on all of the children born in Denmark from 1990 to 1999. The authors prospectively followed the data records of these children until 31 December 2010. Several baseline measurements were taken, including: gender, birthweight, birth complications, diagnosis of intellectual disability, parental education levels, parental employment statuses, parental psychiatric diagnoses, and maternal smoking during pregnancy. Measurements of injuries and emergency ward visits were taken in 4 years: the year before their fifth birthday, and the year after their tenth, eleventh and twelfth birthdays.

All children with ADHD were diagnosed according to the International Classification of Diseases (ICD-10-DCR). Children diagnosed with ADHD before the age of 5 years (n=419), or after the age of 10 years (n=3,743) were excluded from the analysis.

Children with ADHD were categorised as ‘medicated’ if they were prescribed with methylphenidate, dexamphetamine, or atomoxetine for at least 6 months within a given year, before the age of 10 years.

Statistical analyses

Baseline characteristics were compared between children with and without ADHD, and medicated and non-medicated children with ADHD.

The authors used regression analyses to examine the effect of ADHD on the prevalence of injuries, and the effect of stimulant medication on the prevalence of injuries and emergency ward visits in children with ADHD.

In two secondary analyses, the authors analysed the effect of stimulant medication using less stringent criteria. In the first analysis, children who had been prescribed stimulant medication for 6 months after the age of 10 years were also included in the medicated group. In the second analysis, children were categorised as medicated if they had been prescribed stimulant medication at least once between the ages of 5 and 10 years.

Results

710,120 children were born in Denmark between 1990 and 1999. Within this cohort 4,557 children had a clinical diagnosis of ADHD between the ages of 5 and 10 years. There were significant differences between children with and without ADHD on all baseline measurements.

Of the 4,557 children diagnosed with ADHD, 1,457 were treated with stimulant medication and 3,100 were non-medicated. There were several significant differences in baseline characteristics between the groups, most notably, birth complications and maternal smoking during pregnancy were higher in the medicated group.

Children with ADHD sustained more injuries each year than the total cohort of children, as shown in the table below. Children with ADHD had a 30% increased risk of sustaining injuries at age 10 and 12 years compared to control children, as indicated by the positive OR (odds ratio) values.

% of the total study cohort who sustained injuries each year

	Total cohort	Children with ADHD	Adjusted OR (95% confidence interval)
Aged 5 years	10.9%	19.3%	n/a
Aged 10 years	13.2%	15.9%	1.29 (1.22 to 1.37)
Aged 12 years	15.6%	17.8%	1.3 (1.23 to 1.37)

Treatment with stimulant medication was associated with a significantly decreased risk of sustaining injuries. Medicated children were on average 31.5% less likely to sustain an injury at ages 10, 11 and 12 years.

Treatment with stimulant medication was also associated with a significantly decreased prevalence of emergency ward visits. Medicated children were on average 28.4% less likely visit an emergency ward at ages 10, 11 and 12 years.

Secondary analyses revealed that the effects of stimulant medication remained significant when including children who received prescriptions for at least 6 months in any year, and when including children who had received at least one prescription before the age of 10.

Conclusions

The authors conclude that stimulant medication has a protective effect for children with ADHD. This means that children with ADHD are less likely to sustain injuries or visit emergency wards if they were prescribed stimulant medication. These effects were maintained even when more inclusive criteria were used for the medicated group.

Strengths and limitations

This was the first prospective cohort study investigating the effect of stimulant medication on the risk of injuries in children with ADHD. The design of the study benefited from a large sample which was unaffected by sampling biases, because the total population of children with ADHD were studied. The authors were also able to control for confounding variables because data were collected on children from birth, before developing ADHD. In addition, the overall effects of stimulant medication were highly significant and similar results were obtained from two appropriate statistical tests.

However, there were some limitations:

• The study would have benefited from a comparison of emergency ward visits in typically developing children and children with ADHD.
• The authors included self-harm injuries within the analyses and did not report the number of these. This makes it difficult to interpret the mechanisms of how stimulant medication reduces the risk of injuries.
• Finally, in Denmark, stimulant medication can only be prescribed by a specialist and not a general practitioner, unlike the UK. As a result, these children are more thoroughly assessed and may have more severe ADHD compared to the non-medicated group and the medicated population of children in the UK.

Summary

This study demonstrates the significant protective effect of stimulant medication on the risk of injuries in children with ADHD. This effect will need to replicated in the UK because there may be important differences between the two populations. Further research is also required to understand the mechanisms driving this effect.

Links

Primary paper

Dalsgaard S, Leckman JF, Mortensen PB, Nielsen HS, Simonsen M. (2015) Effect of drugs on the risk of injuries in children with attention deficit hyperactivity disorder: A prospective cohort study. Lancet Psychiatry, 2, 702-709. [Abstract]