central nervous system depressant, any drug that decreases the function of the central nervous system, such as alcohol, tranquilizers, barbiturates, and hypnotics. Such drugs can produce tolerance, physical dependence, and compulsive drug use. These substances depress excitable tissue throughout the central nervous system by stabilizing neuronal membranes, decreasing the amount of transmitter released by the nerve impulse, and generally depressing postsynaptic responsiveness and ion movement. Larger dosages cause anesthesia and potentially fatal respiratory and cardiovascular depression. Central nervous system depressants elevate the seizure threshold and can produce physical dependence in a relatively short period. After alcohol the most abused depressants are the short-acting barbiturates, especially pentobarbital, secobarbital, glutethimide, methyprylon, and methaqualone. These substances have popular street names on the illicit market, such as “reds” (secobarbital) and “yellows” (pentobarbital). Sudden withdrawal of general central nervous system depressants that have been used in high doses for prolonged periods can be fatal to some individuals.
