opium, narcotic drug that is obtained from the unripe seedpods of the opium poppy (Papaver somniferum), a plant of the family Papaveraceae. (See poppy.) Opium is obtained by slightly incising the seed capsules of the poppy after the plant’s flower petals have fallen. The slit seedpods exude a milky latex that coagulates and changes color, turning into a gumlike brown mass upon exposure to air. This raw opium may be ground into a powder, sold as lumps, cakes, or bricks, or treated further to obtain derivatives such as morphine, codeine, and heroin. Opium and the drugs obtained from it are called opiates.
The pharmacologically active principles of opium reside in its alkaloids, the most important of which, morphine, constitutes about 10 percent by weight of raw opium. Other active alkaloids such as papaverine and codeine are present in smaller proportions. Opium alkaloids are of two types, depending on chemical structure and action. Morphine, codeine, and thebaine, which represent one type, act upon the central nervous system and are analgesic, narcotic, and potentially addicting compounds. Papaverine, noscapine (formerly called narcotine), and most of the other opium alkaloids act only to relax involuntary (smooth) muscles.