Perhaps because beer, wine, and other alcoholic beverages are so common in everyday life, most people do not think of alcohol as a drug. But alcohol is a drug, a powerful central nervous system depressant that is generally classified with similar drugs such as barbiturates, minor tranquilizers, and general anesthetics. As a depressant, alcohol depresses, or slows down, the operation of the central nervous system, which includes the brain and the spinal cord.

The depressed performance of the central nervous system caused by alcohol consumption creates the slurred speech, impaired physical coordination, and other physical signs that indicate a person has been drinking. But in Under the Influence: A Guide to the Myths and Realities of Alcoholism, authors James R. Milam and Katherine Ketcham explain that this drug is complex in the variety of ways it can affect...