Any substance that slows down normal brain function and reduces overall central nervous system (CNS) arousal is a depressant. Most depressants appear to act on the brain by affecting levels of the neurotransmitter gamma-amino butyric acid (GABA), a neurotransmitter that serves a primarily inhibitory function in the brain (meaning its main action is to decrease the level of brain activity). Depressant medications principally treat anxiety and sleep disorders.
There are two broad categories of depressant medications: benzodiazepines and barbiturates. Benzodiazepines (also widely known as tranquilizers) are primarily prescribed to treat panic attacks, anxiety, and stress; the best-known examples are Valium (diazepam), Librium (chlordiazepoxide HCl), and Xanax (alprazolam). Some benzodiazepines have a greater sedating effect, including Halcion (triazolam) and ProSom (estazolam), which are prescribed for shortterm treatment of sleep disorders. Barbiturates generally have a greater sedating effect than benzodiazepines, and less of an impact on anxiety, so they are used primarily to treat sleep disorders, though they are also sometimes prescribed for anxiety and stress. The best known of the barbiturates include phenobarbital, pentobarbital sodium (Nembutal), and mephobarbital (Mebaral). In high doses, these are sometimes used to produce general anesthesia.
Beyond these prescription drugs, the most widely used depressant in the world is alcohol. Like other depressants, it reduces CNS arousal and has a sedative effect. With all depressants, this translates into slower reaction time, poor judgment, and impaired decision-making, which is why driving under the inﬂuence of alcohol is illegal. That is also the reason why other depressants, including the prescription drugs listed above, as well as milder substances such as antihistamines, usually bear warnings regarding the inadvisability of operating heavy machinery.
At ﬁrst, the person taking a prescription depressant will feel sedated, but within several days that person will become accustomed to the drug and develop a tolerance, needing more of the drug to achieve the same effect. It can therefore be quite dangerous to use barbiturates and benzodiazepines for more than a very short period of time. Once a physical dependence has developed, removal of the drug will lead to withdrawal, which can be especially dangerous with depressants. Since the primary action of a depressant is to slow down the brain’s activity, the brain’s reaction when the individual stops taking it may be a bit of a rebound, with activity racing out of control and possibly causing seizures (this is more likely with barbiturates than with benzodiazepines— withdrawal from the latter is rarely life-threatening). It is important not to take depressants while already taking any other substance that depresses CNS activity, including painkillers, alcohol, or even many over-the-counter allergy medicines. Combining these medicines, especially with alcohol, can slow down breathing or heart rate enough to lead to death.
- Brecher, E. M. Licit and Illicit Drugs; The Consumers Union Report on Narcotics, Stimulants, Depressants, Inhalants, Hallucinogens, and Marijuana— Including Caffeine. New York: Little, Brown & Co., 1974.