opium, substance derived by collecting and drying the milky juice in the unripe seed pods of the opium poppy, Papaver somniferum. Opium varies in color from yellow to dark brown and has a characteristic odor and a bitter taste. Its chief active principle is the alkaloid morphine, a narcotic. Other constituents are the alkaloids codeine, papaverine, and noscapine (narcotine); heroin is synthesized from morphine. Morphine, heroin, and codeine are addicting drugs; papaverine and noscapine are not. A tincture of opium is called laudanum; paregoric is a mixture of opium, alcohol, and camphor.
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