Sex differences in ADHD trajectories across childhood and adolescence

For every girl with ADHD, there are three boys with the same diagnosis. But among adults, the gender ratio is more like 1:1, which is quite a large discrepancy. So what’s going on?

Studies have investigated possible predictors of childhood vs. later (adolescent/adult-onset) ADHD, and they found girls tend to develop ADHD at a later age than boys (Murray, 2017). Now a team that includes the same researchers has investigated this confirming their first conclusion, which could partially explain the discrepancy in the ADHD gender ratio between children and adults. 

The researchers analysed data on 1,571 children living in Zurich, Switzerland, whose teachers used a standard scale to assess symptoms of inattention and also of hyperactivity/impulsivity every year from age 7 (which is the children they started school) through to age 15. The two domains of ADHD were assessed separately, as previous work has found that they can develop at different rates.

60 per cent of the children had low levels of inattention between the ages 7 to 15, whereas the remaining 40 per cent of the boys had persistently high inattention levels during this period.  Among the girls there was more variation, and generally lower symptom levels: almost a third had moderate symptoms that declined with increasing age, while the others started out with relatively serious symptoms at age 7, which then declined, but still remained above average at age 15.

For hyperactivity/impulsivity, there were also some contrasting developmental profiles between the sexes. The majority of children (81 per cent of the girls and 61 per cent of the boys) started out with low levels of symptoms, which decreased even further into late adolescence. Additionally, a group of children (13 per cent of boys and 10 percent of girls) had mildly elevated symptoms in childhood, followed by a dip around age 11 to 13, but then had a rapid increase.  Finally, there was also a group of children (24 per cent of boys, versus only 9 per cent of girls) who had high levels of symptoms all the way through the study period.

So, according to this data, boys show consistently higher levels of ADHD diagnostic criteria- hyperactivity, impulsivity and inattention from a young age.  Whereas, girls tend to develop high levels of these symptoms after adolescence. 

According to the DSM, current ADHD diagnostic criteria for children require symptoms to have begun before the age of 12. This could mean that a greater proportion of girls with ADHD, than boys, are being missed by clinicians. (Exactly why adolescence might be associated with a sudden rise in these symptoms in some children, and especially girls, is not known – it could be to do with hormones, and/or increased social and academic pressures.) 

This provided supporting evidence that there are sex differences in symptoms of ADHD trajectories that have potentially important implications for clinical practice. Specifically, to guard against under-identification of females, later symptoms should now be considered in the diagnostic criteria and indicators should be more suitable for adolescence and adulthood. 

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