Youngest in Class Most Likely to Receive ADHD Medication

A new Australian study finds that children born closer to the cutoff date for a given school class are prescribed attention deficit/hyperactivity disorder (ADHD) more often than their months-older peers.

Examining de-identified data from over 300,000 children in Western Australia, they split the vast cohort into two groups, one of children aged 6-10 (born between July 2003 and June 2008) and another of children aged 11-15 (born July 1998 to June 2003). Nearly 2% (5,937 students) overall received some form of ADHD medication, with boys three times more likely to be prescribed than girls.

They found a striking difference in likelihood of treatment based on age relative to classmates. Those born in June, the final recommended birth month for intake in an Australian school year, were twice as likely in the 6-10 group to receive ADHD medicine as those born in the first intake month. Relative risk was 1.93 in boys (95% CI 1.53-2.38) and 2.11 for girls (95% CI, 1.57-2.53).

The numbers were a bit less surprising in the 11-15 year old group, but they still showed a jump: the relative risk for boys was 1.26 (95% CI, 1.03-1.52), and for girls it was 1.43 (95% CI, 1.15-1.76). The researchers saw consistency when the cohort was combined, and also when first three months and last three months of school intake were compared.

The authors of the study cited a number of other studies that found similar phenomenon, including three from North America and one from Taiwan. The Taiwanese study reported a similar overall diagnosis rate (1.6%), though the three North American studies produced drastically increased overall rates, ranging from 3.6% to 5.8% (the lowest of those three was a Canadian study).

The report references the writings of Allen Frances, the American psychologist known for his role in the creation of the much-discussed Diagnostic and Statistical Manual of Mental Disorders IV (DSM-IV), who in a 2015 letter wrote that he believed a 2% overall ADHD diagnosis rate “would best balance harms and benefits.”

The critical words with which Frances opened that letter are not mentioned in the Australian report: “It is scandalous that the ADHD diagnosis is made so loosely and that treatment is prescribed so recklessly,” he wrote, worrying that children were receiving prescriptions “often without clear indication, without the slightest idea of its long-term impact and without informed consent.”

The new open-access report, “Influence of birth month on the probability of Western Australian children being treated for ADHD,” was published this month by The Medical Journal of Australia.

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