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Attention-deficit/hyperactivity disorder: Overview

Key points

  • Attention-deficit/hyperactivity disorder (ADHD) is a chronic neurodevelopmental disorder characterized by inattention, disorganization and/or hyperactivity or impulsivity.
  • ADHD is the most common neurodevelopmental disorder in children.
  • Educators are often the first to notice symptoms of ADHD in children.
  • ADHD persists into adulthood for at least 60% of children with the disorder.
  • People with ADHD often have difficulty regulating emotional responses, and become easily angered or frustrated.
  • Adults with ADHD may self-medicate with caffeine, nicotine, cannabis or cocaine.
  • ADHD requires long-term planning and should include the primary care provider as well as a psychiatrist.
  • There is no one treatment for ADHD and medication should not be considered in isolation of other treatments.


Everyone may experience symptoms of ADHD at some point in their lives, but the Diagnostic and Statistical Manual of Mental Disorders (DSM) outlines criteria that must be met for a diagnosis of ADHD. Several symptoms must be present and causing impairment in two or more settings (e.g., home, school, work, play).

ADHD is characterized by symptoms of inattention and/or hyperactivity or impulsivity.

Symptoms of inattention include:

  • failing to pay attention to details or making careless mistakes in schoolwork or at work
  • having difficulty sustaining attention in tasks or at play
  • seeming not to listen when spoken to directly
  • not always following through on instructions and failing to complete schoolwork, chores or workplace tasks
  • experiencing difficulty organizing tasks and activities
  • avoiding, disliking or being reluctant to engage in tasks that require sustained mental effort
  • losing things necessary for tasks or activities
  • being distracted by extraneous stimuli
  • often being forgetful in daily activities.

Symptoms of impulsivity include:

  • fidgeting or squirming
  • being unable to stay seated
  • running or climbing in inappropriate situations
  • being unable to play quietly
  • talking excessively
  • blurting out answers or finishing other people's sentences
  • having trouble waiting to take turns
  • interrupting or intruding on others.


  • ADHD affects about one in 20 children.
  • Symptoms persist into adulthood in at least 60% of children.
  • ADHD is more common in boys than girls.
  • Comorbid disorders are common in people with ADHD. They include oppositional defiant disorder, conduct disorder, anxiety disorders, depression and specific learning disorder.


It is not clear exactly what causes ADHD, but it appears to be caused primarily by genetic factors. Environmental factors may also play a role.

Genetic factors

  • Several international studies show that ADHD often runs in families. It is likely that most cases of ADHD are inherited.
  • A child who has a parent with ADHD has more than a 50% chance of developing ADHD.
  • Several genes are likely involved. Research shows that the brains of people with ADHD work differently than those of people without the disorder. There are differences in neurotransmitters, as well as less activity in some parts of the brain. The frontal lobes, which control decision making, also work differently.

Environmental factors

  • Studies show that children born to mothers who smoked or drank alcohol during pregnancy are more likely to have ADHD.
  • Children exposed to high levels of lead have a higher risk of developing ADHD.


  • ADHD is highly treatable.
  • People with ADHD can function well if they receive effective treatments and interventions.
  • Some characteristics of ADHD, such as impulsivity, hyperactivity and inattention, can lead people with the disorder to successful careers if they are used productively. The clinician can help to identify those attributes and possible careers.

Evidence summary

American Psychiatric Association. (2013). Diagnostic and Statistical Manual of Mental Disorders (5th ed.). Washington, DC: Author.

Canadian ADHD Resource Alliance. (2011). Canadian ADHD Practice Guidelines (3rd ed.). Toronto, ON: Author.

Jain, U. (2011). The adult patient with ADHD. In D. Goldbloom & J. Davine (Eds.), Psychiatry in Primary Care: A Concise Canadian Pocket Guide (pp. 191–206). Toronto, ON: Centre for Addiction and Mental Health.

National Institute of Mental Health. (2012). Attention Deficit Hyperactivity Disorder (ADHD). Bethesda, MA: Author.