Attention Deficit Hyperactivity Disorder (ADHD) is the most common behavioral disorder of childhood because of the large of the prevalence of the disorder. This disorder does not only affect children, but it also is the problem of teens, adolescents and adults. This disorder is complex, neurodevelopmental disorder with many symptoms, treatments, medications, side effect of medications. ADHD is very complex. Over past several years, scientists and researchers have not known exactly ADHD’s causes. Some individuals still do not believe ADHD’s existence. This disorder has various types. Not all people who have the disorder have the same type. Some of them may be hyperactive. Others may have problems with attention. Others might be between inattentive and impulsive. Therefore, the best understanding of the disorder is as a group of behavioral symptoms that reflect attentions (including selective attention and sustain attention), hyperactivity, and impulsivity. Symptoms are believed to be link to the prefrontal cortex. Some patients can have some or all of the following: anterior cingulate cortex, which is result in symptoms of inattention (forgetting things, losing things, careless mistakes, not listening and not pay attention to details), dorsolateral prefrontal cortex, which is linked to sustain attention and inability to solve problems, prefrontal motor ADHD 2 cortex which is linked to hyperactivity, and orbital frontal cortex which involves in impulsivity. In people with the disorder, the certain brain areas have less activities and blood flow; the brain structure is smaller than normal people. Several genes have been implicated in ADHD involving dopamine (neurotransmitter) transporters, dopamine receptors, dopamine beta hydroxylase, and some serotonin receptors/ transporters. When neurotransmitters do not work the way they are suppose to, the brain system will not function inefficiently. That is why people in the disorder cannot control their behaviors.