Content Source: Centers for Disease Control and Prevention
There are three different types of ADHD, depending on which symptoms are strongest in the individual:
- Predominantly Inattentive Type: It is hard for the individual to organize or finish a task, to pay attention to details, or to follow instructions or conversations. The person is easily distracted or forgets details of daily routines.
- Predominantly Hyperactive-Impulsive Type: The person fidgets and talks a lot. It is hard to sit still for long (e.g., for a meal or while doing homework). Smaller children may run, jump or climb constantly. The individual feels restless and has trouble with impulsivity. Someone who is impulsive may interrupt others a lot, grab things from people, or speak at inappropriate times. It is hard for the person to wait their turn or listen to directions. A person with impulsiveness may have more accidents and injuries than others.
- Combined Type: Symptoms of the above two types are equally present in the person.
Causes of ADHD
Scientists are studying cause(s) and risk factors in an effort to find better ways to manage and reduce the chances of a person having ADHD. The cause(s) and risk factors for ADHD are unknown, but current research shows that genetics plays an important role. Recent studies of twins link genes with ADHD.
In addition to genetics, scientists are studying other possible causes and risk factors including:
- Brain injury
- Environmental exposures (e.g., lead)
- Alcohol and tobacco use during pregnancy
- Premature delivery
- Low birth weight
Research does not support the popularly held views that ADHD is caused by eating too much sugar, watching too much television, parenting, or social and environmental factors such as poverty or family chaos. Of course, many things, including these, might make symptoms worse, especially in certain people. But the evidence is not strong enough to conclude that they are the main causes of ADHD.
For more information about cause(s) and risk factors, visit the National Resource Center on ADHD or the National Institute of Mental Health.