ADHD seems to be something of a buzz-word in the press: recently we were told that being overweight, taking paracetamol or having a diet high in fat and sugar during pregnancy all increase the likelihood of your child having ADHD. But are ADHD prevalence rates really increasing in the UK? Here we will examine figures and put that in the context of global prevalence rates.
What is ADHD?
ADHD is a neurodevelopmental difference (that is, a difference in the way the brain develops as children grow up), which is defined by behaviour. The major features are higher levels of impulsivity, hyperactivity, and inattention than are seen in their same-aged peers. Children with the predominantly inattentive subtype (the most common) are more distractable and can have difficulty controlling their attention, but don’t show high levels of hyperactive or compulsive behaviour. By contrast, those with the predominantly hyperactive type show high levels of physical activity and can have difficulty regulating their behaviour. A further group of children show elevated hyperactivity as well as attention difficulties and are described as having a mixed subtype.
For a diagnosis to be made, the children’s attention difficulties or activity levels must create difficulties for the child in at least two settings, for example at home and at school, for at least six months, between the ages of 6 and 12 years.
Is ADHD on the rise? It depends who you ask!
Prevalence estimates for ADHD vary quite substantially depending on a number of factors, including when and in what country the estimate was published, and the criteria for a diagnosis; for example, if diagnosis is based on medication rates or parent report and whether (if either) the ICD or DSM diagnostic classification criteria were used[ii]. The highest ever recorded estimate has been for 4-17 year old Colombian boys, 19.8% of whom were classified as having ADHD[iii].
A 2007 study, which combined published reports from around the world, estimated prevalence to be between 5.9 – 7.1% in children and adolescents[iv]. More recently, this work was updated to explore how global prevalence has changed in the past ~30 years[v]. The team examined 154 studies published between 1985 and 2012, all of which included children and adolescents under 18 years of age. This analysis revealed some fascinating insights: with only studies that defined ADHD according to strict clinical criteria, prevalence remained virtually unchanged from 1985 to 2012. However, what did make a difference to prevalence estimates was who reported children’s status: for example, when teacher report was used, prevalence was on average 5.47% higher than when best-estimates based on clinical criteria were used. Type of clinical criteria used also had an impact, with studies using ICD-10 reporting 4.09% lower prevalence than studies using DSM-IV (see endnote 2).
More evidence that it matters who you ask comes from a telephone survey published in the USA in 2010[vi] in which parents of 4-17 year olds were asked whether they had ever been told by a doctor or other healthcare professional that their child had Attention Deficit Disorder (ADD) or ADHD. This survey was conducted once in 2003 and again in 2007 and between those points, reported that lifetime prevalence (whether the parent had ever been told that their child had the disorder) increased from 7.8% to 9.5%. Of the parents reporting ADD or ADHD in 2007, two thirds also reported that their child was on medication for the disorder. The most recent data from parent report in the USA put prevalence at a steady 9.5%[vii].
So it seems that while the percentage of children with ADHD defined by strict clinical guidelines is not changing, it is true that, in America at least, the number of parents being told that their child has the disorder is increasing.
A note on co-occurring conditions
Many children with ADHD have one or more other neurodevelopmental or mental health condition(s). Estimates vary substantially, but somewhere between 10-70% of children with ADHD are reported to also have autism[viii] [ix]. However, before 2015, children assessed using the DSM could not, by definition, receive a dual diagnosis of autism and ADHD. The shift to dual diagnosis might explain some of the increase in ADHD rates seen in America, where the DSM is a mainstay used to inform ADHD diagnoses.
Co-occurring conditions can also mask ADHD symptoms. For example, it may be more difficult to identify ADHD symptoms in a child with severe anxiety compared to a child with ADHD but no mental health issues. Therefore, it is likely that we are still underestimating the actual prevalence of ADHD in schools because of the frequency with which it co-occurs with other conditions.
What about ADHD in the UK?
We can assume that in the UK, just like the rest of the world, the percentage of children who actually have ADHD remains steady. So what percentage are diagnosed with the disorder and what percentage are on medication?
As part of the Millennium Cohort Study[x], researchers replicated the American telephone survey for parents[xi], asking whether parents had ever been told that their child has ADD or ADHD. Just 1.4% of the 13,586 children asked about had been given a diagnosis at some point (2.2 % of boys and 0.5 % of girls). Given that the children were just 6-8 years old at the time of this survey, the figure of 1.4% is likely to underestimate UK diagnosis rates over the whole of childhood. However, an equivalent study of 5-9 year olds in America gave a prevalence estimate of 6.3%[xii], suggesting that diagnosis rates in the UK are low and may well undershoot true prevalence rates by some margin.
In order to look at how diagnosis has changed in the UK, we can look at medication rates. Three substances are currently licensed to treat ADHD in the UK: the stimulants methylphenidate (most usually the brand Ritalin) and dexamphetamine, as well as the non-stimulant medication, atomoxetine. Despite headlines such as ‘use of ADHD drugs increases by 50% in six years’[xiii], the actual rates of medication prescription are very low in this country. Figures from GPs in the NHS have shown that in 1995 just 0.015% (1 in 6,667) of under 16 year olds had ever been given medication for ADHD, with this figure rising to 0.5% (1 in 200) by 2008 and stabilising at that level up to 2013[xiv]. Of those children who were given medication, 77% were still medicated after one year and 60% after two years- relatively long stretches of medication in comparison to global norms. A separate study of NHS patients over six years of age found very similar changes in medication rates[xv], and further showed that male patients aged 6-12 had the highest rates of medication, while females aged 6-12 showed the highest increase in medication rates.
So, for the moment at least, not only do diagnosis rates in the UK seem to be fairly stable, but they are also lower than would be anticipated given global prevalence. Indeed, one study found that fewer than one in three children with ADHD accesses specialist care in the UK[xvi]. One potential reason for this is that in the UK health disorders are classified according to criteria set out in the ICD rather than the DSM, with the ICD being slightly narrower in its definition of the disorder[xvii]. In addition, there are also likely to be cultural and financial forces driving this phenomenon.
There are some really interesting issues left unsolved in the field of ADHD research, including the fact that around three times as many boys than girls are diagnosed. This may be because the same diagnostic criteria are used to diagnose the disorder in both genders, which is arguably inappropriate. Support for this idea comes from research which suggests that girls require additional emotional and behavioural problems[xviii] or more severe ADHD symptoms than boys in order to be diagnosed[xix]. Other on-going debates centre around the influence that changing societal expectations have on how parents and teachers view ‘appropriate behaviour’, as well as how different cultures view the role that diagnosis and medication have to play in children’s mental health.
The verdict here is, largely speaking, a neuro-myth: although rates of ADHD diagnosis and medication have changed considerably since the 80s, they seem to have remained stable for about a decade. Notably though, recent and upcoming changes to classification criteria mean that this story is still unfolding. In a way the core of this question is really whether rates of ADHD in the UK are being artificially inflated by the media and big pharma. In response, we can safely say that, if anything, there are a significant number of children in UK schools whose attention difficulties are currently underestimated.
If you are interested in why there might be increasing numbers of children with other special educational needs in UK schools, see this recent blog by Dr. Jo Van Herwegen.
The ADHD institute website gives wealth of information and advice: http://www.adhd-institute.com/
[i] Barkley, R. A. (2002). Major life activity and health outcomes associated with attention-deficit/hyperactivity disorder. The Journal of Clinical Psychiatry, 63(Suppl12), 10-15.
[ii] The International Classification of Diseases (ICD) and the Diagnostic and Statistical Manual for Mental Disorders (DSM) are both classification systems which define the diagnostic criteria for known mental health disorders (the ICD also covers all physical conditions). The ICD is published by the World Health Organisation and is currently in its 10th edition; it is used by all WHO member states, including the USA. By contrast, the DSM, which is currently in its 5th edition, is published by the American Psychiatric Association and is largely only used clinically in the USA. The two classification systems are similar with respect to the classification of mental health disorders but are not identical, such that discrepancies can occur where one or other requires more or more severe behavioural symptoms in order to receive a diagnosis.
[iii] Pineda, D. A., Lopera, F., Palacio, J. D., Ramirez, D., & Henao, G. C. (2003). Prevalence estimations of attention-deficit/hyperactivity disorder: differential diagnoses and comorbidities in a Colombian sample. International Journal of Neuroscience, 113(1), 49-71.
[iv] Willcutt, E. G. (2012). The prevalence of DSM-IV attention-deficit/hyperactivity disorder: a meta-analytic review. Neurotherapeutics, 9, 490–499.
[v] Polanczyk, G. V., Willcutt, E. G., Salum, G. A., Kieling, C., & Rohde, L. A. (2014). ADHD prevalence estimates across three decades: an updated systematic review and meta-regression analysis. International Journal of Epidemiology, 43 (2), 434-442. DOI: 10.1093/ije/dyt261
[vi] Centres for Disease Control and Prevention. (2010). Increasing prevalence of parent-reported attention-deficit/hyperactivity disorder among children – United States, 2003 and 2007. Morbidity and Mortality Weekly Report, 59, 1439-1443.
[vii] Pastor PN, Reuben CA, Duran CR, Hawkins LD. Association between diagnosed ADHD and selected characteristics among children aged 4–17 years: United States, 2011–2013. NCHS data brief, no 201. Hyattsville, MD: National Center for Health Statistics. 2015.
[viii] Zablotsky, B., Bramlett, M. D., & Blumberg, S. J. (2020). The co-occurrence of autism spectrum disorder in children with ADHD. Journal of Attention Disorders, 24(1), 94-103.
[ix] Kaat, A. J., Gadow, K. D., & Lecavalier, L. (2013). Psychiatric symptom impairment in children with autism spectrum disorders. Journal of Abnormal Child Psychology, 41(6), 959-969.
[x] A multi-discipliniary, longitudinal research study following the lives of around 19,000 children born in the UK in 2000-2001: http://www.cls.ioe.ac.uk/page.aspx?sitesectionid=851
[xi] Russell, G., Rodgers, L.R., Ukoumunne, O.C., & Ford, T. (2014). Prevalence of Parent-Reported ASD and ADHD in the UK: Findings from the Millennium Cohort Study. Journal of Autism and Developmental Disorders, 44, 31. doi:10.1007/s10803-013-1849-0
[xii] National Centre for Health and Statistics. (2012). Health, United States, 2011: With special feature on socioeconomic status and health. Hyattsville, MD: Centres for Disease Control and Prevention. Retrieved from http://www.cdc.gov.ezproxy.york.ac/nchs/hus.htm
[xiv] Beau-Lejdstrom, R., Douglas, I., Evans SJW, & Smeeth, L. (2016). Latest trends in ADHD drug prescribing patterns in children in the UK: prevalence, incidence and persistence. British Medical Journal Open, 6:e010508. doi: 10.1136/bmjopen-2015-010508
[xv] McCarthy, S., Wilton, L., Murray, M. L., Hodgkins, P., Asherson, P., & Wong, I. C. K. (2012). The epidemiology of pharmacologically treated attention deficit hyperactivity disorder (ADHD) in children, adolescents and adults in UK primary care. BioMed Central, Pediatrics, 12, 78. DOI: 10.1186/1471-2431-12-78
[xvi] Sayal, K., Goodman, R., & Ford, T. (2006). UK Barriers to the identification of children with attention deficit/hyperactivity disorder. Journal of Child Psychology and Psychiatry, 47(7), 744-50.
[xvii] Tripp, G., Luk, S. L., Schaughency, E. A., & Singh, R. (1999). DSM-IV and ICD-10: a comparison of the correlates of ADHD and hyperkinetic disorder. Journal of the American Academy of Child and Adolescent Psychiatry, 38 (2), 156-164.
[xviii] Mowlem, F., Agnew-Blais, J., Taylor, E., & Asherson, P. (2019). Do different factors influence whether girls versus boys meet ADHD diagnostic criteria? Sex differences among children with high ADHD symptoms. Psychiatry Research, 272, 765-773.
[xix] De Rossi, P., Pretelli, I., Menghini, D., D’Aiello, B., Di Vara, S., & Vicari, S. (2022). Gender-Related Clinical Characteristics in Children and Adolescents with ADHD. Journal of Clinical Medicine, 11(2), 385.