Addiction is a primary, complex brain disorder. It is characterized by compulsive drug seeking and use, despite harmful consequences, and by long-lasting chemical changes in the brain which interfere with a person’s ability to think clearly, exercise good judgment, control behavior, and feel normal without using drugs. Addiction is often (but not always) accompanied by physical dependence, a withdrawal syndrome, and a need for increasing amounts of the substance to achieve the same effect. For many people, addiction becomes chronic, with relapses possible even after long periods of abstinence.