Subcategories of attention deficit hyperactivity disorder.

It is estimated that as many as 20% of school-aged children have an attention deficit hyperactivity disorder (ADHD). Hyperactivity is recognized as a common symptom of a variety of childhood disorders. In many instances the symptoms of ADHD signal the onset of severe psychopathology and indicate comorbidity. Because a significant number of children exhibiting symptoms of ADHD are unresponsive to stimulants or have side effects, the use of such drugs is contraindicated. In this article we describe ADHD according to subcategories in an effort to distinguish diverse groups of children with ADHD and to identify those responding best to psychopharmacologic agents other than stimulants. Further understanding of the neurobiology of ADHD is needed to more clearly define and treat this condition.