The body’s physical and/or psychological addiction to a psychoactive (mind-altering) substance, such as narcotics, alcohol, or nicotine. Physical dependency on such chemicals as prescription drugs or alcohol stems from repetitive use followed by the gradual increase in the body’s tolerance to, or ability to assimilate, that drug. Thus, increasingly larger doses must be consumed to maintain the drug’s desired effects, which may include the temporary alleviation of depression or anxiety, or the induction of euphoria. Without an increase in the dosage, it is possible for actual or anticipated drug withdrawal symptoms to occur.