Attention Deficit Hyperactivity Disorder (ADHD) affects 5% of children and 4% of adults across Europe.
ADHD is a neuro-developmental disorder, which means that the condition is underlined by a different balance of brain chemicals and is present from birth, and so the brain develops differently to the “typical” brain. However, it is really important to remember that “different” doesn’t necessarily mean “bad”; unless, of course, that difference is misunderstood and goes without the right supports, interventions, and accommodations. Indeed, the difference associated with ADHD can create a lot of problems for people with the condition, because they must live, work, and go to school in a world created for the typically developing person.
People with ADHD are likely to be creative, flexible thinkers with a lot of energy and spontaneity. However, things which someone without ADHD might find easy, like remembering important items or thinking before they speak, can be very challenging for someone with ADHD. As a result, places like school and the workplace can require skills that people with ADHD often do not have (e.g., organisation, time-management, and sustaining attention) which may lead to problems in education and employment, such as underachievement and risk of exclusion and dismissal.
It’s important to remember that ADHD is a spectrum disorder. This means that ADHD symptoms (i.e., hyperactivity, impulsivity, and/or inattention) are not exactly the same in every person. So, one person might be very active, talk a lot and interrupt and intrude on other people; another person could daydream and be quiet and withdrawn; another person could be both: all of them could still have ADHD.
“So you think you know about ADHD?” Watch this for a different perspective.
ADHD is the most prevalent neuropsychiatric disorder in childhood, as it occurs in 3-7% of school-age children, and displays by high heritability of 60-80% , which means that it has a strong genetic background.
Its main symptoms are restlessness, fidgetiness, lack of attention and concentration as well as increased impulsivity. The latter is also a hallmark of ADHD in adulthood, and persistence of the disorder can be found in approximately 65% of affected children .
Of the two main symptom domains, inattentiveness and hyperactivity/impulsivity, our own studies show the latter to strongly share genetic liability with oppositional behaviour . The hyperactive-impulsive ADHD subtype is associated with aggression  and goes along with a highly increased risk for aggressive behaviour . Especially impulsive aggression is frequently observed in ADHD , potentially mediated by difficulties with control of behaviour and emotional dysregulation (irritable and aggressive moods)  .
Treatment of aggression with stimulant medication has been investigated in children with ADHD and demonstrated to be effective, with an average effect size around 0.8   . Not surprisingly, the presence of co-morbid CD further facilitates aggressive behaviour. Accordingly, an ADHD polygenic score was recently shown to be significantly associated with co-morbid CD, which is explained by aggression symptoms .
This suggests that aggression in ADHD indexes genetic and clinical severity. Increased aggression in ADHD opens up a negative developmental trajectory: increased ADHD frequency is observed in detained adolescents   and in young adult male prison inmates, as much as 45% were found to suffer from ADHD .
Our own research found a 6-fold increase in violent and aggressive incidents among male prisoners associated with current ADHD, even after controlling for antisocial personality disorder . Importantly, anti-ADHD medication in adulthood results in a significant reduction in the criminality rate , which was 4-fold higher in ADHD compared to controls. This underscores the importance of ADHD diagnosis and treatment in aggression and criminal behaviour.