The same narcotic may be either an analgesic or a hypnotic, depending on the dosage. Narcotics produce an analgesic effect by interacting with specific nerve cells called receptors in the central nervous system. Several chemicals that occur naturally in the body, including endorphins and enkephalins, interact with the same receptors. Scientists believe these naturally occurring chemicals control the brain's perception of pain. See Endorphin .
Narcotic drugs are extremely useful in medicine, but they also have dangerous effects.
Large doses of narcotics may cause death. The careless use of opium and substances made from it to relieve pain has frequently caused a drug habit. No one should use these and other narcotics except under the direction of a physician. The United States carefully regulates the importation of narcotics as well as the manufacture and distribution of narcotic by-products. Physicians must state certain facts on narcotic prescriptions, and druggists must keep records of them.