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Higher ADHD diagnosis and prescriptions for children born in July and August, research finds

Posted on 4 September 2024

Children born in July and August are at least 40% more likely to be diagnosed with - and to receive prescriptions for - attention deficit hyperactivity disorder (ADHD), than children born in September and October, new research has found.

In England, most children start school full-time in the September after their fourth birthday, resulting in almost a year’s difference in age between children who are in the same school year, but either born just before and after September 1st. 

The team analysed anonymised data from GP surgeries and hospitals, focusing on 96,698 children born between 2002 and 2010 in either July, August, September or October. Half were boys and half girls, with a representative mix of ethnicities. 

They found that by age 15, around 1.6% of the children were diagnosed with ADHD and about 1.25% were also prescribed drugs for ADHD.

Increase

The researchers then compared ADHD diagnoses and prescriptions between the ‘early’ starters born in July and August and the ‘late’ starters born in the following months.

They found that by age 15, around 1.5% of early starters were receiving prescriptions for ADHD, compared to just 1% of late starters. This equates to an increase of 50% in ADHD prescriptions for early compared to late starters. 

Even after controlling for differences in characteristics between children within the two groups, the researchers still found a large percentage increase in ADHD prescriptions for children born in July and August. This equates to a 40% greater likelihood of an ADHD prescription for early, compared to late, starters. 

Similarly, they found that by age 15, children are 40% more likely to be diagnosed with ADHD if born in July and August. These gaps in ADHD rates are even larger for young children. 

Need to understand

This finding alone didn’t surprise the researchers, according to Professor Cheti Nicoletti from the University of York: “We’ve seen this disparity in previous research in other countries, so we expected to see something similar here,” she said. “What we really need to understand is what causes such a disparity.”

The study highlights that the disparity in ADHD prescriptions between children born in July-August and in September-October is mainly explained by a peer-comparison bias caused by differences in relative age among classmates. 

The study also finds that the gap in ADHD prescriptions, observed from age nine onward, is mainly driven by drug prescriptions initiated in the first years of primary school and by the fact that children tend to continue the ADHD pharmacological treatment for several years after its initiation. 

Indeed, the authors found that among children who initiated prescriptions between age five and eight, 86.16% are still prescribed drugs for ADHD at age nine, 83.98% at 10, 81.29% at 11, 82.75% at 12, 74.63% at 13, 70.21% at 14, 64.20% at 15.

Disappears with age

Co-author Dr Catia Nicodemo from the University of Oxford said: “The good news is that from age nine onward, there is no difference in the initiation of ADHD prescriptions between children born in July-August and in September-October, which means that the peer-comparison bias disappears with age.” 

“The bad news is that potential biases in pharmacological treatments initiated in the first years of primary school persist at later age.” 

Co-author Dr Joaquim Vidiella-Martin from the University of Oxford said: “We can’t definitively identify whether there is an over-diagnosis of children born in July-August or an under-diagnosis of children born in September-October or just more marginal diagnoses for July-August born, but we can say that a  gap in pharmacological treatment between between children born in July-August and in September-October suggests an inefficient and unfair use of medical resources.”

Overlooked

Drawing on their findings, the researchers then provide some suggestions on how to reduce the gap in prescriptions. They say that delaying school for children born over the summer months would not work as a blanket policy, as it could mean ADHD is even more likely to be overlooked in some already under diagnosed groups of children.

Instead, they offer two other recommendations for parents, teachers and policymakers. 

The first is to make parents and teachers more aware of ADHD symptoms and improve diagnosis particularly between the ages of 5-8 where the discrepancy between groups is the greatest. 

The second is that when four-year-olds first begin full-time school, there are at least two start dates across the year, so children can be grouped with others they are closest to in age with a maximum of six months difference between them.

 

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