opiate drug, any of a group of drugs derived from opium. Used medicinally to relieve pain and induce sleep, they include codeine, morphine, the morphine derivative heroin, and, formerly, laudanum. Sometimes included in the group are certain synthetic drugs that have morphinelike pharmacological action. All opiates are considered controlled substances by U.S. law and are available only by prescription. Heroin is not available legally at all in the United States. See also narcotics.