ADHD: not just a childhood disorder?

Jessica Agnew-Blais, recipient of the 2016 Janice Sinson Award, explains her groundbreaking research into the development of ADHD in adulthood.

Attention deficit hyperactivity disorder (ADHD) was once considered to be a childhood-only disorder. When children with a diagnosis of ADHD grow up, they will also grow out of ADHD.

We know now that this is not necessarily the case: ADHD can continue into adulthood. In fact, ADHD occurs in around 2.5% of the adult population and is associated with poor outcomes such as unemployment, substance abuse and even higher mortality rates.1,2,3

Nevertheless, it is still widely accepted that ADHD has a childhood onset: an adult may have ADHD but it is presumed to have begun in childhood. For example, the American Psychiatric Association’s manual of mental disorders states that in order for a clinician to make a diagnosis of adult ADHD, symptoms should have begun before age 12.4 However, there is little evidence to support whether it is truly the case that all people with adult ADHD had the disorder as children.


Attention Deficit Hyperactivity Disorder - or ADHD - is thought to be caused by a chemical imbalance in the brain that affects attention, concentration and impulsivity.

Someone with ADHD might have significant attention problems, appear restless, fidgety, overactive and impulsive. They can act before thinking and often speak before thinking by blurting out and interrupting others.

Read more about ADHD

In my recent research, we looked at this question using data from a study that followed over 2,000 people from ages 5 to 18. My colleagues and I found that among people who had ADHD at age 18, nearly 70% did not meet the diagnostic criteria in childhood (at ages 5, 7, 10 or 12, based on mother and teacher reports collected when participants were children).5 This suggested that ADHD can begin in adulthood.

This was surprising given the aforementioned assumption of adult ADHD as a continuation of childhood ADHD. Additionally, we found that people with late-onset ADHD were equally impaired compared with people whose childhood ADHD persisted into adulthood, with lower overall life satisfaction and higher rates of other mental health problems such as anxiety and depression.

Jessica Agnew-Blais discusses her research with our staff.

Why the onset of ADHD in adulthood?

One possible explanation is that people with late-onset ADHD could have shown ADHD in childhood, but the disorder was masked by protective factors such as a very supportive family environment.

Second, maybe other mental health problems could mimic the symptoms of ADHD: for example, severe anxiety might lead to problems paying attention. However, we found that about one-third of people with late-onset ADHD did not have any other common mental health problem that could explain their ADHD symptoms.

Another explanation could be that it is possible that late-onset ADHD is a different disorder from childhood ADHD. Late-onset ADHD could have different causes and underlying biology than ADHD that begins in childhood. Maybe environmental factors are at play more throughout adolescence and leading into adulthood. Future research will begin to disentangle these different explanations for late-onset ADHD.


Our research has important implications for young adults living with ADHD. Because many clinicians conceptualise and diagnose ADHD as a childhood-onset disorder, adults who seek treatment may be turned away if they do not report having ADHD in childhood.

However, given our findings that a majority of people with ADHD in young adulthood did not exhibit the disorder in childhood and that these individuals were equally impaired as those with childhood ADHD, the absence of a childhood ADHD diagnosis should not stop adults from receiving professional support. 

With any mental health condition early intervention is vital – a failure to diagnose can prolong or even worsen symptoms. Our research points at a need to raise awareness of the fact that ADHD can develop beyond childhood.

Going forward, we hope to better understand risk factors for late-onset ADHD, which may help prevent its onset. If we can identify individuals at high risk for developing late-onset ADHD, perhaps early interventions could address symptoms before they become a full-fledged disorder in the transition to young adulthood.

Read Jessica's research paper (Word document)


  1. Simon V, Czobor P, Balint S, Meszaros A, Bitter I.  Prevalence and correlates of adult attention-deficit hyperactivity disorder: meta-analysis. British Journal of Psychiatry. 2009 Feb;194 (3) 204-211.
  2. Kessler RC1, Adler L, Barkley R, Biederman J, Conners CK, Demler O, Faraone SV, Greenhill LL, Howes MJ, Secnik K, Spencer T, Ustun TB, Walters EE, Zaslavsky AM. The prevalence and correlates of adult ADHD in the United States: results from the National Comorbidity Survey Replication. American Journal of Psychiatry. 2006 Apr;163(4):716-23.
  3. Dalsgaard S, Østergaard SD, Leckman JF, Mortensen PB, Pedersen MG. Mortality in children, adolescents, and adults with attention deficit hyperactivity disorder: a nationwide cohort study. Lancet. 2015 May;385(9983):2190-6. 
  4. American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Arlington, VA: American Psychiatric Publishing.
  5. Agnew-Blais JC, Polanczyk GV, Danese Am Wertz J, Moffitt TE, Arseneault L. Evaluation of the persistence, remission, and emergence of attention-deficit/hyperactivity disorder in young adulthood. JAMA Psychiatry. 2016 Jul;73(7):713-20.