Adult ADHD is prevalent, seriously impairing and highly comorbid. Despite this, it is under-recognised and under-treated across 20 countries and cultures, according to a report from the World Health Organization (WHO) World Mental Health (WMH) surveys.*
The WMH surveys were a series of cross-national community epidemiological surveys enabling pooled cross-national analyses of prevalence and correlates of common mental disorders. Face-to-face interviews were administered in two parts:
- Part I, administered to all respondents (n=90,172), assessed core Diagnostic and Statistical Manual of Mental Disorders – 4th edition (DSM-IV) mental disorders using the WHO Composite International Diagnostic Interview (CIDI) version 3.0, a fully structured lay-administered interview. The CIDI retrospective assessment of childhood ADHD was based on the Diagnostic Interview Schedule.
- Respondents with symptoms of childhood ADHD were asked if they still had issues with inattention or impulsivity-hyperactivity and, if so, any associated impairments were assessed using the 19-item modified version of the WHO Disability Assessment Schedule 2.0.† Additionally, respondents were asked about the number of days out of the past 30 in which they were unable to carry out their normal activities due to problems with their physical or mental health.
- Part II assessed additional disorders and correlates. Part II was administered to those Part I respondents meeting lifetime criteria for a DSM-IV mental disorder (ADHD was assessed among adults aged 18–44 years; n=26,744). All respondents were asked whether they received treatment for ‘‘problems with your emotions or nerves or your use of alcohol or drugs’’ in the 12 months prior to interview from four different treatment sectors.‡
Mean prevalence of DSM-IV/CIDI ADHD in childhood was 2.2% (range 0.1–8.1%) across the surveys. Prevalence was deemed to be significantly related to country income level, with prevalence of 3.3% in high-, 2.2% in upper–middle- and 0.6% in low-/lower–middle-income countries (p<0.001). Sub-threshold childhood ADHD (defined as 4–5 rather than 6+ inattention and/or hyperactivity/impulsivity symptoms) was prevalent in 3.7% of participants (4.7% in high-, 4.0% in upper–middle- and 2.2% in low-/lower–middle-income countries; p<0.001).
Adult ADHD was observed in 57.0% of those with a history of childhood ADHD and 41.1% of those with a history of sub-threshold childhood ADHD (no significant differences were observed related to country income level; p=0.30 and p=0.14, respectively). Current prevalence of adult ADHD in the total sample was estimated at 2.8% (range 0.6–7.3%), with higher prevalence in high-income countries (3.6%) and upper–middle-income (3.0%) than low-/lower–middle-income (1.4%) countries (p<0.001).
Pooled results from this survey also indicated the following:
- Childhood ADHD was significantly more common among men than women (odds ratio, 1.6; 95% confidence interval 1.3–2.0), and was positively associated with level of educational attainment (p<0.001).
- Persistence of childhood ADHD into adulthood among childhood cases was significantly associated with respondent employment status (employed vs all others; p=0.001), due to comparatively low persistence among the currently employed. There were no significant differences observed in sociodemographic criteria related to adult ADHD among sub-threshold childhood cases.
- 12-month adult ADHD was significantly associated with comorbid disorders, and odds ratios ranged between 2.5 for major depressive disorder and 15.0 for oppositional defiant disorder (p<0.05).
- Adults with ADHD were more likely to have disability in cognition (21.8%) than in self-care (4.8%), social interactions (10.8%) or mobility (15.5%).
- 21.8% of respondents with 12-month ADHD received some treatment for mental health problems in the 12 months before interview, and this was significantly related to country income level (28.8% in high-, 15.5% in upper–middle- and 6.8% in low-/lower–middle-income countries; p<0.001).
Key limitations of this study were that adult ADHD was estimated from an imputation model rather than directly and childhood ADHD was assessed retrospectively. However, these results support earlier findings that adult ADHD is prevalent, highly comorbid and may cause serious impairment.
Read more about the prevalence of adult ADHD here
*The surveys included 11 countries classified by the World Bank as high-income countries (national surveys in Belgium, France, Germany, Italy, the Netherlands, Northern Ireland, Poland, Portugal, Spain and the USA, along with a regional survey in Spain [Murcia]), five upper–middle-income countries/areas (national surveys in Lebanon and Romania, a survey in urbanised areas of Mexico and regional surveys in Brazil [Sao Paulo] and Colombia [Medellin]) and four low-/lower–middle-income countries (national surveys in Colombia and Iraq, a survey in urbanised areas of Peru and a regional survey in the People’s Republic of China [Shenzhen]). Colombia was listed as both an upper–middle- and lower–middle-income country in two different surveys because Colombia’s World Bank rating changed between the times of the two surveys
†A validated self-report instrument that assesses difficulties in four domains of role functioning over the past 30 days before interview: cognition (communicating and understanding); mobility (moving and getting around); self-care (personal hygiene, dressing, eating, living alone); and social interaction. The assessment includes a series of parallel questions about frequency and severity of impairment (rated none, mild, moderate and severe) in each role domain
‡Mental health speciality (psychiatrist, psychologist, social worker or counsellor in a mental health speciality setting, use of a mental health hotline); general medical (primary care doctor, other general medical doctor, nurse, any other health professional); human services (religious or spiritual advisor, social worker or counsellor in any setting other than a speciality mental health setting); and complementary-alternative medicine (any other type of healer, such as a chiropractor or native healer, or participation in an Internet support group or self-help group)
Fayyad J, Sampson NA, Hwang I, et al. The descriptive epidemiology of DSM-IV Adult ADHD in the World Health Organization World Mental Health Surveys. Atten Defic Hyperact Disord 2017; 9: 47-65.