Youngest children in class more likely to be diagnosed with ADHD

A study of Canadian children found that the youngest children in the class are significantly more likely to be diagnosed with attention-deficit/hyperactivity disorder (ADHD) and prescribed medication than their peers in the same grade.

To determine the effect of relative age within a grade on diagnosis and pharmacologic treatment of ADHD, researchers studied a cohort of 937,943 children in British Columbia, where cutoff for entry into kindergarten or grade 1 is December 31. The children were aged between 6 and 12 years at any point during the 11-year study.

The proportion of children diagnosed or treated for ADHD increased with each birth month from January to September and then plateaued until December. Boys born in December were 30% more likely to be diagnosed with ADHD than boys born in January. Girls born in December were 70% more likely to be diagnosed with ADHD than girls born in January. Similarly, the likelihood of being prescribed a medication to treat ADHD was greater for boys (41%) and girls (77%) born in December than for those born in January.

The researchers say that this relative-age effect, consistent with findings in US children, raises concerns about overdiagnosis and overtreatment of ADHD in younger children within a grade because of the potential harmful effects. Unnecessary prescribing exposes children to adverse effects on sleep, appetite, and growth, as well as an increased risk of cardiovascular events. Inappropriate diagnosis can adversely affect the child’s self-perception and change the way adults treat them.

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