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ADHD is a chronic behavioral disorder of childhood onset (by age seven). ADHD affects children, adolescents, and adults. It is characterized by behavior that is hyperactive, impulsive, or inattentive. There are several different types of ADHD. Some children are primarily inattentive and don't display signs of hyperactivity. Others, however, are hyperactive and/or impulsive. The rest exhibit a mixture of these symptoms.

The cause of ADHD is not known at this time, but brain chemistry, genetics, and environmental factors may all play roles in the development of ADHD.

It is estimated that almost 8% of American children have ADHD (about 1-3 children in every classroom of 30 children). About 60% of children with ADHD will continue to experience trouble related to their disorder into adulthood.

Because so many cases of ADHD are diagnosed in childhood, the information provided here is geared toward children.