Opioid dependence is the modern diagnostic term for narcotic addiction, but the older term is still often used. This entry, however, uses the modern term. The term opioid refers to natural and synthetic substances that have morphine-like effects. The term opiate is generally used in a more restricted sense to refer to MORPHINE, HEROIN, CODEINE, and similar drugs derived from OPIUM. OPIOID dependence is defined as a cluster of symptoms related to continued use of an opioid drug. One of the prominent features of the disorder is the inability to stop using the drug. Persons with repeated periods of opioid dependence are often called narcotic addicts. Because they are not always dependent (that is, addicted), the term opioid users seems more suitable and therefore is used here. During the late nineteenth and early twentieth...