Attention deficit hyperactivity disorder (ADHD) is a problem of not being able to focus, being overactive, not being able control behavior, or a combination of these. For these problems to be diagnosed as ADHD, they must be out of the normal range for a person's age and development.
ADHD usually begins in childhood but may continue into the adult years. It is the most commonly diagnosed behavioral disorder in children. ADHD is diagnosed much more often in boys than in girls.
It is not clear what causes ADHD. A combination of genes and environmental factors likely plays a role in the development of the condition. Imaging studies suggest that the brains of children with ADHD are different from those of children without ADHD.
Symptoms of ADHD fall into three groups:
Some people with ADHD have mainly inattentive symptoms. Some have mainly hyperactive and impulsive symptoms. Others have a combination of different symptom types. Those with mostly inattentive symptoms are sometimes said to have attention deficit disorder (ADD). They tend to be less disruptive and are more likely not to be diagnosed with ADHD.