Drugs and Substances: Learn It 2—Alcohol and Other Depressants

Depressants

depressants

A depressant is a drug that tends to suppress central nervous system activity. Depressants include ethanol (alcohol), barbiturates, and benzodiazepines.

 

These drugs share a common ability to serve as agonists of the gamma-Aminobutyric acid (GABA) neurotransmitter system (agonists enhance the effect of the signaling molecule by activating their receptors). Because GABA has a quieting effect on the brain, GABA agonists also have a quieting effect; these types of drugs are often prescribed to treat both anxiety and insomnia.

An illustration of a GABA-gated chloride channel in a cell membrane shows receptor sites for barbiturate, benzodiazepine, GABA, alcohol, and neurosteroids, as well as three negatively-charged chloride ions passing through the channel. Each drug type has a specific shape, such as triangular, rectangular or square, which corresponds to a similarly shaped receptor spot.
Figure 1. The GABA-gated chloride (Cl-) channel is embedded in the cell membrane of certain neurons. The channel has multiple receptor sites where alcohol, barbiturates, and benzodiazepines bind to exert their effects. The binding of these molecules opens the chloride channel, allowing negatively-charged chloride ions (Cl-) into the neuron’s cell body. Changing its charge in a negative direction pushes the neuron away from firing; thus, activating a GABA neuron has a quieting effect on the brain.

Effects of Depressant Use

The use of alcohol results in a variety of changes to consciousness. Alcohol intoxication is measured for legal and medical uses in terms of Blood Alcohol Content (BAC). A BAC of 0.10 (0.10% or one-tenth of one percent) means that there are 0.10 g of alcohol for every 100 ml of blood. While a BAC of 0.0 is sober, in the United States a BAC of 0.08 is legally intoxicated, and above that is considered very impaired. BAC levels above 0.40 are potentially fatal.

At rather low doses, alcohol use is associated with feelings of euphoria as it slows the activity of the sympathetic nervous system and often makes people feel less inhibited. As the dose increases, people report feeling sedated. Generally, alcohol is associated with decreases in reaction time and visual acuity, lower levels of alertness, and a reduction in behavioral control.

With excessive alcohol consumption, above .20 and beyond, a person might experience dizziness, nausea, a complete loss of consciousness, and/or difficulty remembering events that occurred during a period of intoxication (McKim & Hancock, 2013).

If a pregnant woman consumes alcohol, her infant may be born with a cluster of birth defects and symptoms collectively called fetal alcohol spectrum disorder (FASD) or fetal alcohol syndrome (FAS).

With repeated use of many central nervous system depressants, such as alcohol, a person becomes physically dependent upon the substance and will exhibit signs of both tolerance and withdrawal. Psychological dependence on these drugs is also possible. Therefore, the abuse potential of central nervous system depressants is relatively high.

Drug withdrawal is usually an aversive experience, and it can be a life-threatening process in individuals who have a long history of very high doses of alcohol and/or barbiturates. This is of such concern that people who are trying to overcome a very serious addiction to these substances should do so under medical supervision.