Addiction is an inability to control the ingestion or inhalation of a drug or other substance, resulting in physiological or psychological dependence. Symptoms of addiction include craving and habitual or compulsive behavior. It is most frequently associated with drug addiction. In a medical context, addiction requires a physical dependence. When the dose of a drug is reduced or withdrawn from the user, the addict experiences withdrawal symptoms. Psychological dependence on activities such as gambling or exercise are difficult to distinguish from a personality disorder or mania. The wide variety of theories on addiction, such as the psychological theory of addictive personality or the physiological concentration on the brain, give rise to a range of therapeutic treatments.