Attention deficit disorder

Attention deficit hyperactivity disorder (ADHD) and attention deficit hyperactivity disorder (ADHD) have probably been around forever, experts say. However, it was not described clinically until the beginning of the 20th century. He has known several names: from hyperactive child syndrome (first appearance in the Diagnostic and Statistical Manual of Mental Disorders in 1968), through attention deficit disorder with or without hyperactivity (1980) and attention deficit hyperactivity disorder or ADHD (1987).

Today, we use the terms attention deficit hyperactivity disorder (ADHD), or attention deficit disorder with or without hyperactivity (ADHD), adopted in 2000 in Quebec, which we have used for this fact sheet.

People with Attention Deficit Hyperactivity Disorder (ADHD) have difficulty concentrating, paying attention, and completing even complex tasks. They often have trouble staying still, taking their turn, and frequently act impulsively.

Attention Deficit Disorder: Understanding It All In 2 Min

While these behaviors can be found in all human beings, they are unusually pronounced and prolonged in those with ADHD. They are also present in all circumstances of life (not just at school or just at home, for example).

ADHD in adolescents and adults

ADHD is often noticed more in children than in adults. It has also been studied much more in children. However, it persists into adolescence in 40% to 70% of cases and into adulthood in half of the children who have it8. It is estimated that about 4% of adults have ADD with or without hyperactivity. Sometimes ADHD is not diagnosed until adulthood.

Three symptoms characterize ADHD: inattention, hyperactivity and impulsivity. They can be present to varying degrees. For example, a child who is always "in the moon", who does not finish his homework, who does not remember instructions and who constantly loses his personal belongings, but who is not particularly agitated could have ADHD. Another, mostly hyperactive, impulsive and restless, but who can concentrate relatively well when tasks interest him might also be affected. In general, hyperactivity and impulsivity are more pronounced in boys than in girls.

In the vast majority of people with ADHD, ADHD has a neurological origin which may depend on heredity and environmental factors. Experts are clear on this: ADHD is not caused by unmet emotional needs or psychosocial issues, although it can be exacerbated by these factors.

ADHD is usually diagnosed around age 7. However, children with ADHD have difficult behaviors before they start school, often as young as 2 years old.

ADHD and intelligence

There is no link between ADHD and a child's intelligence. The academic difficulties that most children with ADHD experience are most often related to behavioral problems or attention deficit, but not to a lack of intelligence.


It is the most common neurobehavioral disorder in children: 5% to 10% of them are thought to have it. It has long been argued that its prevalence is higher in boys, possibly because boys with ADHD exhibit more hyperactive behavior, which is more easily noticed than girls (in whom inattention is predominant). However, the most recent studies do not seem to reveal any significant differences between the sexes.


It is not easy to diagnose ADHD, as the same symptoms can result from other disorders more or less closely related to ADHD. Therefore, the diagnosis of ADHD will be based on a thorough evaluation of the child and his living environment.

The doctor is primarily interested in the psychomotor development of the child. Parents are encouraged to draw up a history of the child's development. Psychological and neuropsychological tests can also be useful in order to assess his IQ and his potential for academic learning. Teachers can also help with the child's assessment. The latter is finally questioned about his current difficulties.

There is no neurological or psychological test that can formally diagnose the disease. According to American Psychiatric Association criteria, a number of symptoms of inattention or hyperactivity / impulsivity must be observed in a child for ADHD to be diagnosed.

For the diagnosis to be confirmed, it is important to know that:

some symptoms should be present before the age of 7;

symptoms should be felt at home as well as at daycare (nursery) or school, although their intensity may vary from place to place;

symptoms should have been present for at least 6 months.


ADHD is a complex disease that does not have a single cause. It is a neurological disorder linked to abnormalities in the development and functioning of the brain.

For example, researchers have observed that in children or adults with ADHD, the areas of the brain responsible for attention, organization and movement control are activated abnormally or have a unique anatomy. They also noted an imbalance in the levels of certain chemical messengers (neurotransmitters) in the brain, such as dopamine and norepinephrine.


Hereditary factors are a major contributor to the development of ADHD. In fact, in studies of identical twins, researchers have found that when one twin has ADHD, in 80% of cases, the other does too. Additionally, most children with ADHD have at least one family member who also has ADHD. In total, a quarter of parents with a history of ADHD have children who also have ADHD36. Several genes involved in ADHD have been identified, but genetic factors alone do not explain the disease.

The environment

Exposure to certain toxic substances (alcohol, tobacco, lead, pesticides, etc.) during fetal life would explain 10% to 15% of cases3. Other environmental factors, not all identified, probably contribute to the onset of the disease in genetically predisposed children.

Brain damage

Brain injury or infection, lack of oxygen at birth, or other birth complications can increase your risk for ADHD. See the People at Risk and Risk Factors sections.

Associated disorders

Many children with ADHD also have some of the following disorders.

Oppositional defiant disorder. Hostile, suspicious and negative attitude towards authority figures which tends to manifest itself more frequently in impulsive and hyperactive children.

Conduct disorders. Profound anti-social behavior which can result in theft of property, fighting-seeking, and generally destructive behavior towards humans and animals.

Depression. Often present, depression results from the rejection that the child experiences because he cannot control himself. He often suffers from low self-esteem. Depression can develop in both children and adults with ADHD - especially if other family members have had it.

Anxiety disorders. Excessive anxiety and nervousness which is accompanied by various physical symptoms (tics, rapid heartbeat, sweating, dizziness, etc.) or obsessive-compulsive disorder.

Learning disabilities. About 20% of children with ADHD have delays in the development of language and fine motor skills (including writing) and need special education.


In adulthood, ADHD can cause serious behavioral and social problems. Thus, nearly half of adults with ADHD suffer from anxiety disorders, which disrupt their social integration and their life balance. Additionally, people with ADHD are more likely than others to be addicted to alcohol or drugs.

It is therefore very important to do everything possible to detect and treat ADHD in the best possible way from childhood.