Influence of birth month on the probability of Western Australian children being treated for ADHD.

Four international studies have found that the youngest children in a school class are more likely than their classmates to receive pharmacological treatment for attention deficit/hyperactivity disorder (ADHD). We investigated whether this late birth date effect applies to children in Western Australia. We compared the proportions of WA children born in the early and late months of a recommended school-year intake who received at least one Pharmaceutical Benefits Scheme prescription for an ADHD medication in 2013.