THE ALCOHOL PRESENT in beer, wine, whiskey, and other liquors is known as ethyl alcohol, or ethanol. Ethanol is a thin, colorless liquid with a strong aroma that has a dramatic effect on the nervous system. It is formed naturally when tiny living organisms known as yeast react with sugars at warm temperatures.

Entering the bloodstream

When a person drinks alcoholic beverages, the ethanol quickly enters the bloodstream without being chemically changed in any way. About 20 percent of it passes directly into the bloodstream from the stomach; the rest is absorbed through the small intestines. The speed with which it is absorbed depends on a number of factors. For example, the absorption rate is slower when food is present in the stomach. Also, alcohol mixed with other liquids such as water or soda is absorbed more slowly than...