ADHD, also called attention-deficit disorder, is a behavior disorder, usually first diagnosed in childhood, that is characterized by inattention, impulsivity, and, in some cases, hyperactivity. These symptoms usually occur together; however, one may occur without the other(s).
The symptoms of hyperactivity, when present, are almost always apparent by the age of 7 and may be apparent in very young preschoolers. Inattention or attention-deficit may not be evident until a child faces the expectations of elementary school.
Three major types of ADHD include the following:
ADHD, combined type
This, the most common type of ADHD, is characterized by impulsive and hyperactive behaviors as well as inattention and distractibility.
ADHD, impulsive/hyperactive type
This, the least common type of ADHD, is characterized by impulsive and hyperactive behaviors without inattention and distractibility.
ADHD, inattentive and distractible type
This type of AHD is characterized predominately by inattention and distractibility without hyperactivity.