Attention-deficit hyperactivity disorder (ADHD), a common neurobehavioural disorder characterized by inattention, hyperactivity and impulsivity, is a chronic disorder and often persists into adulthood. CNS stimulants have been the most well known treatment for ADHD for several decades due to their high effectiveness, good safety profiles and relatively minor adverse effects. Non-stimulant agents, including atomoxetine, extended-release guanfacine and extended-release clonidine (US FDA approved), and several non-FDA-approved agents, such as bupropion and tricyclic antidepressants (TCAs), were recently proven to be effective alternatives to the stimulants in several open-label and placebo-controlled trials. However, most medication trials for ADHD have been short term and thus have not provided information on the long-term outcomes of ADHD treatment. Since the medical treatment of many children with ADHD, especially those with more severe symptoms or co-morbid disorders, has to be continued for several years, recent studies have shifted their focus from the acute effectiveness of stimulants or non-stimulant drugs to the long-term outcomes of medications for ADHD. Evidence has shown that stimulants, along with the non-stimulants atomoxetine and extended-release guanfacine, are continuously effective for 24-month treatment periods with few and tolerable adverse effects.