Alcohol: Chemistry

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Alcohol occurs naturally when fruits, vegetables, and grains exposed to bacteria in the air undergo the process of fermentation. People can create and speed up the conditions for fermentation to produce ethyl alcohol, also called ethanol. Pure ethanol is not drinkable but is an ingredient of alcoholic beverages, such as beer, wine, and liquors. The concentration of ethanol in beer is approximately 4 to 5 percent; in wine it is 11 to 12 percent; and in most liquors it is 40 to 50 percent. Also, alcoholic beverages are often diluted by water before they are consumed.

Ethanol acts as a depressant on the central nervous system, which is made up of the brain and spinal cord. This means it slows brain and nervous system function. It produces sedation and even sleep at higher doses. When people drink a moderate amount of ethanol, they may feel an initial stimulation or rush of energy. But soon after that first phase, alcohol decreases memory, the ability to concentrate, quickness of reaction, and judgment.

When a person drinks a beverage that has alcohol in it, the ethanol is absorbed from the stomach by simple diffusion into the blood-stream. Strong drinks with a higher percentage of alcohol are absorbed more quickly, while beer and wine are absorbed more slowly. Food slows the absorption process. Peak blood alcohol concentration occurs within thirty to ninety minutes of drinking—earlier on an empty stomach and later on a full stomach. Once absorbed, ethanol spreads throughout the parts of the body that contain water, going wherever water goes.

Recent evidence suggests that low or moderate amounts of ethanol (one to two drinks per day) can indirectly reduce the risk of heart attacks. The doses must be low enough to avoid liver damage. Scientists believe that this beneficial effect occurs because alcohol raises the level of a certain type of cholesterol in the blood. This cholesterol slows the development of arteriosclerosis, often the cause of heart attacks.

Tolerance develops to a drug when the dose must be increased to achieve the effect of the original dose. Tolerance to ethanol can occur in just a few weeks or may take years, depending on how much and how consistently a person drinks. Like tolerance, dependence on ethanol can develop after only a few weeks of consistent drinking. When a dependent person stops drinking, he or she experiences withdrawal symptoms. These symptoms include the "shakes," hallucinations, nausea, vomiting, diarrhea, fever, sweating, and sometimes convulsions. Several days after the last drink, an individual sometimes goes through a severe phase of withdrawal called the delirium tremens. Symptoms of this last phase of withdrawal include confusion, disorientation, and vivid hallucinations.

Accidents and Injuries from Alcohol; Alcohol: Complications of Problem Drinking; Alcohol: Withdrawal; Alcohol Treatment: Behavioral Approaches; Alcohol Treatment: Medications; Blood Alcohol Concentration.