Attention deficit hyperactivity disorder (ADHD) is a disorder that affects behavior. It can cause hyperactive and impulsive behavior, and/or make it difficult to pay attention. These behavioral problems continue over a long period of time. ADHD affects children, adolescents, and adults.

There are three types of ADHD:

  • Inattentive (classic "ADD")
  • Hyperactive-impulsive
  • Combined—the most common type

The cause of ADHD is unknown. It most likely is caused by a chemical imbalance in the brain. There also appears to be a genetic factor since ADHD can run in families.

Child's Brain
Child Brain
A chemical imbalance in the brain may be responsible for ADHD.
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