Many patients with ADHD have long suffered under the impression that they just have a "character problem" or "just need to work harder," when in fact they have an inherited and treatable problem. On the other hand, not all patients with difficulties in attention and distractibility have ADHD; depression, anxiety, learning disabilities, substance abuse and sleep disorders can all cause similar difficulties and should not be treated with ADHD medications. And in some cases there can be a mismatch between a person's talents and their chosen career that can manifest as problems with focus and task completion.

ADHD is characterized by difficulty initiating or completing tasks, sustaining attention, and controlling impulsive actions. Patients may have difficulties with organization and time management. As a result of these difficulties, the disorder can have serious negative impacts on the educational, social, and occupational lives of those who suffer from its symptoms.

Three types of ADHD are diagnosed:

• Combined inattentive and hyperactive-impulsive (this is the most common type, found in about 80% percent of patients).
• Predominantly inattentive (about 15%).
• Predominantly hyperactive-impulsive (about 5%)

The terminology can be confusing. Attention Deficit Disorder (ADD) is an older term for what is now called Attention-Deficit/Hyperactivity Disorder (ADHD). There is no longer any actual disorder “officially” called ADD, but some people still use ADD (or Adult ADD) to refer to the type ADHD that is predominantly inattentive, and use ADHD (or Adult ADHD) for the type of ADHD that is predominantly hyperactive or impulsive. However, these all refer to the same disorder, and the treatments are the same.

Although the exact mechanism is unknown, a number of associated neurochemical abnormalities have been observed, and considerable evidence suggests that the disorder has a strong genetic component and a biological underpinning; the pathophysiology includes dysfunction in both norepinephrine and dopamine activity. Pharmacotherapy (medication treatment) remains the best established and most effective treatment for most patients. For some patients, psychosocial interventions, such as exercise, cognitive-behavior therapy or coaching may provide additional important benefits.