The three major categories of drugs used to treat ADHD are psychostimulants, alpha-2 adrenergic agonists and antidepressants.

Psychostimulants, more commonly referred to as simply "stimulants," inhibit the reabsorption of dopamine. Dopamine is a neurotransmitter that helps to keep the central nervous system functioning normally. This leaves more dopamine circulating in the body. Stimulants are the mainstay of ADHD medication treatment, and up to 90 percent of people who take them report at least some improvement in symptoms like impulsivity and hyperactivity, according to the American Psychiatric Association. Although these drugs have a stimulating effect on most people, they are calming in those with ADHD.

Stimulants usually work fairly rapidly, with symptom reduction beginning between 30 and 45 minutes after ingestion. They work for between four and 12 hours and are typically taken two to three times daily. Some longer-acting formulations, known as extended release versions, may be taken just once a day. Most of the stimulants are only recommended for children over age 6. However, some amphetamines may be prescribed to children over age 3. The stimulant pemoline, which was once prescribed for ADHD, was withdrawn from the market in 2005 because it may cause serious side effects, including liver damage.

Alpha-2 adrenergic agonists are sometimes used to treat core ADHD symptoms, but more often are used to reduce irritability and aggression and to treat body tics related to ADHD. They can also be used to promote sleep in people who report insomnia.