The four major categories of drugs used to treat attention deficit hyperactivity disorder (ADHD) are psychostimulants, alpha-2 adrenergic agonists, antidepressants and norepinephrine reuptake inhibitors.

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

Stimulants usually work fairly rapidly, with symptom reduction beginning between 30 and 45 minutes after ingestion. They work for between 4 and 12 hours and are typically taken two to three times daily. Some longer-acting (extended release) formulations 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 is no longer used to treat ADHD because it may cause serious side effects that may harm the liver. It was withdrawn from the market in 2005.

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

Depression is a disorder commonly associated with ADHD, and antidepressants are often prescribed to treat lasting feelings of sadness. In addition, antidepressants that increase the availability of the neurotransmitters dopamine and norepinephrine in the body appear to be effective in treating core symptoms of ADHD. The tricylcic antidepressants and the dopamine-norepinephrine reuptake inhibitor bupropion appear to be particularly effective in treating ADHD. The drug atomoxetine is technically an antidepressant approved to treat ADHD, although it is not approved to treat depression. Many of the other non-stimulant medication used for ADHD are approved for other purposes, such as treating depression and high blood pressure. They are prescribed for patients with ADHD as part of the common practice of “off-label” prescriptions.

Antidepressants are sometimes used to treat ADHD in patients who do not tolerate stimulants well. These drugs only have to be taken once daily. They are prescribed far more often in adults than in children. Selective serotonin reuptake inhibitors (SSRIs), often used to treat depression and anxiety, have not been effective in treating the symptoms of ADHD.

Patients should be aware that a physician may need to adjust the dosage or change medications to achieve the best results with minimal side effects. In addition, the U.S. Food and Drug Administration (FDA) has advised that antidepressants may increase the risk of suicidal thinking in some patients and all people being treated with them should be monitored closely for unusual changes in behavior.

*The drug atomoxetine is not approved for use as an antidepressant by the FDA.