Neuropsychological functioning in ADHD: Are girls different from boys?
Rates of ADHD Among Girls
Just boys have ADHD, right? Wrong. ADHD can affect girls, with recent estimates of ratios ranging from 2:1 to 6:1. Staller and Faraone  estimated that 32 million females worldwide have ADHD based on current information on prevalence and sex ratios, making the diagnosis of ADHD in females a major public health concern. This gender difference in prevalence, along with the likelihood of a referral bias that continues to under identify ADHD in females, has resulted in a much slower growing body of literature on the female ADHD profile. For a long time we largely didn’t know if the significant and global deficits that have been documented in boys with ADHD, such as having a hard time processing information, holding information on line, estimating time, and stopping a behavior once started [2-6], could be extrapolated to girls.
ADHD Symptoms in Girls
Along with the belief that ADHD doesn’t happen in girls came some studies suggesting that even if girls had ADHD, they weren’t as impaired as boys with ADHD . These findings have since been disconfirmed and evidence is building that we can no longer ignore. Studies over the last decade consistently show that females struggle in similar ways to boys – forgetting things they need for school, having problems with speech and language, solving complex problems, having a hard time putting on the brakes, losing track of time, making more errors in their work and struggling academically [8-10]. This overall lack of gender differences in cognitive functioning has also been documented in an adult sample .
Some even find that girls with ADHD are more compromised in their intellectual functioning and may have poorer knowledge of vocabulary [12,13]. Lower scores on Block Design, a measure of perceptual and visual spatial reasoning, have been noted in ADHD girls compared to ADHD boys with performance on all other measure of cognitive functioning falling similarly across gender . However other studies show that in some areas, boys may have more problems. For example, research on a New Zealand population found that although adolescent girls and boys with ADHD were struggling similarly cognitively , there was one noted difference: ADHD males showed evidence of greater inhibition than ADHD females – in other words, boys with ADHD may struggle more with stopping themselves once they have started. Newcorn and his colleagues  found the same thing: their sample of girls with ADHD made fewer impulsivity errors (commission errors) than the ADHD boys.
In sum, although there are fewer females being diagnosed with ADHD, most studies have found few or no cognitive differences across the sexes in ADHD populations [17,18] with significant cognitive impairments across most areas of functioning (planning, set-shifting, working memory, attention, processing speed, executive function, naming speed, etc) evident in both males and females with ADHD compared with individuals without ADHD [11,15] [8,19,20]. However, stimulant medications (like Ritalin) have been known to influence outcomes of some studies (e.g., ), emphasizing the importance of considering the effect that medications can have on the results that have been reported. This finding also confirms that medications may be able to help with some of these complex academic activities. Overall though, the bulk of research to date is telling us one thing: don’t ignore the ADHD girls, they need help. More similarities than differences have been noted between the sexes in ADHD populations and therefore, we can expect similar problems in ADHD individuals, regardless of the sex of the individual concerned.
There is some evidence to suggest that males and females with ADHD may have different neural substrates for their behaviors, explaining why developmental differences exist (like girls exhibiting more attentional problems and less hyperactivity compared with boys). Hermens et al.  determined that women with ADHD (and not men) had substantially reduced skin conductance (a measure of autonomic arousal) whereas men with ADHD (and not women) had increased EEG theta activity (an inverse measure of arousal). Further research may show that distinct mechanisms may underpin the behaviour across the sexes, accentuating the importance of not assuming that findings in males with ADHD can be extrapolated to females with ADHD. In other words, parents need to be aware that some of the widely accepted information about ADHD may only apply to boys .