Epidemiology
Prevalence:
Studies in different populations have found similar prevalence estimates. In the US, the prevalence has been estimated at 4.4%; in Canada, 3% to 6%; and in France, 4% to 5%.[4][5][6][7] Another large study stratified the prevalence of attention deficit hyperactivity disorder (ADHD; in people ages 18-44 years) across low- and high-income countries. With an overall average of 3.4% (range 1.2% to 7.3%), the study found a lower prevalence in lower-income countries (1.9%) compared with higher-income countries (4.2%).[8]
In one study of electronic health records in California from 2007 to 2016, the prevalence of ADHD in adults doubled over a decade from 0.43% to 0.96%.[9]
Although prevalence appears to have increased substantially in recent decades, meta-regression analyses suggest that this difference is due to differences between studies and that, in fact, prevalence has remained stable worldwide since the 1980s.[10][11]
There is some evidence from prospective follow-up studies of representative community samples that a new diagnosis of ADHD may emerge during adolescence or in early adulthood.[12] These findings are not universally accepted, due to methodological concerns, although it is generally accepted that children with subthreshold symptoms may then go on to fully meet the diagnostic criteria for ADHD as adolescents/adults.[13]
A study of college students found the prevalence of ADHD among this population to be 4%.[14]
Rates in adults have been estimated at around 2.5% to 2.8% overall, with higher rates in high- (3.6%) and upper-middle (3.0%) than low-/lower-middle (1.4%) income countries.[15][16]
Among those diagnosed with ADHD as children, by age 25 years, only 15% retain the full ADHD diagnosis, although a much larger proportion (65%) fulfill the Diagnostic and Statistical Manual of Mental Disorders criteria for ADHD in partial remission.[17][18]
ADHD was found in a Dutch population study to persist in older adults ages 60 years and over, with a prevalence of 2.8% to 4.2% depending on symptom cutoff, and was found to be associated with substantial functional impairment and mental health comorbidity in this age group.[19]
In a 2014 survey in England, using a self-report scale, 1 in 10 adult respondents screened positive for ADHD (meaning they required a fuller assessment). While the actual prevalence of ADHD will be lower than 1 in 10, these findings suggest that ADHD characteristics are widespread in the adult population.[20]
Studies have found that primary care physicians may be less likely than psychiatrists to diagnose adult ADHD.[14]
Presentations:
According to a phone population screen of adults, combined and hyperactive-impulsive presentations of ADHD are less common among adults than inattentive ADHD.[14]
Comorbidity:
About 75% of adults with ADHD will have at least one other mental health disorder.[2]
Patients also frequently demonstrate features of other neurodevelopmental disorders, including autism spectrum disorder, dyslexia, dyscalculia, and dyspraxia. Anxiety, mood (depression and bipolar disorder), and substance use disorders are the most common co-occurring psychiatric conditions.[9][21][22]
Sex disparities:
In children, ADHD is diagnosed far more commonly in boys than girls with a ratio of 5:1; in the adult population, while the diagnosis remains positively associated with being male, the rate is less skewed.[23] More recent studies report a male-to-female ratio closer to 3:1, maybe as a result of better diagnosis in females by clinicians.[24] Among adults, the male-to-female ratio is reported to be approximately 3:2.[5] A national survey for DSM-IV disorder prevalence identified 61.6% of adults with ADHD as men.[5] Girls with ADHD demonstrate more inattentive-type symptoms with a later onset of impairment. It is also suggested that girls with ADHD may internalize their problems more and, therefore, go undiagnosed.
Ethnic disparities:
Class differences:
Adult ADHD is more common among those previously married and those who are unemployed or disabled.[5]
In general, adults with ADHD have lower levels of academic attainment and poorer career prospects than those without ADHD.[1]
Geographic differences:
According to phone diagnostic screenings, there is a higher concentration of adults with ADHD in urban areas, specifically in northeastern and north central states.[5]
Obesity:
There is evidence for a significant association between the presence of ADHD and obesity/being overweight.[25]
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