opium, Organic compound, a narcotic drug known since ancient Greek times, obtained from exuded juice of immature fruit capsules of the opium poppy. Opium has legitimate medical uses, as the source of the alkaloids codeine and morphine and their derivatives. It is also used illicitly, either raw or purified as alkaloids and their derivatives (including heroin). Opium alkaloids of one type (e.g., morphine, codeine) act on the nervous system, mimicking the effects of endorphins; they are analgesic, narcotic, and potentially addicting (see drug addiction). Those of a second type, including papaverine and noscapine, relieve smooth muscle spasms and are not analgesic, narcotic, or addicting. Habitual opium use produces physical and mental deterioration and shortens life. Overdose can cause death by depressing respiration.