Nervous system depressants are substances that decrease, or depress, the function of the nervous system. There is an expansive variety of prescription and recreational drugs that act as central nervous system depressants. Depression of the central nervous system, which includes the brain, results in a decreased rate of breathing and a decreased heart rate, and if the depression is substantial, can lead to unconsciousness, coma, or death. Decreased function of the peripheral nervous system tends to lead to loss of sensation, pain, or lack of muscular control throughout the body. Loss of function in the peripheral nervous system, however, is seldom referred to as nervous system depression — nervous system depressants almost always refer to substances that depress the central nervous system.
Many different types of central nervous system depressants are prescribed to treat conditions such as anxiety, sleep disorders, and acute stress disorder. Some are also used as anesthetics, tranquillizers, sedatives, and anticonvulsants. Common drugs that depress the central nervous system include barbiturates, which are used for treating anxiety, sleep disorders, and other conditions, and benzodiazepines, which are used for similar purposes and are also useful as muscle relaxants. While depressants can work through a variety of different mechanisms, many tend to increase the activity of the neurotransmitter gamma-Aminobutyric acid, or GABA. GABA inhibits nervous system activity, so increased expression of GABA depresses the nervous system.
One of the most common nervous system depressants is ethanol, the alcohol that is contained in alcoholic beverages. The depressant effects of alcohol tend to manifest in the form of sluggish response time, clumsiness, and slurred speech. Highly excessive alcohol consumption can also cause blackouts, unconsciousness, and death. Alcohol consumption is culturally and socially significant in many different parts of the world, and many people find it to be quite pleasant, but it is not without its risks. It can be particularly dangerous when consumed in conjunction with other nervous system depressants, as this can result in dangerously low nervous system activity.
Mixing different nervous system depressants, alcohol or otherwise, is generally considered to be an inadvisable practice. The central nervous system controls many important bodily functions, including the maintenance and regulation of heart rate. Excessive use of nervous system depressants can, therefore, cause the heart to stop, leading to death. People who do overdose on such depressants require rapid care to maintain circulation. Health professionals must often artificially maintain both the heart rate and breathing of an individual who has overdosed on drugs that depress the central nervous system.