Although anyone can become intoxicated while drinking, the alcoholic is less likely to recognize the signs and control his or her intake. Intoxication is produced by alcohol as it circulates in the blood and acts to depress the central nervous system (see depressant). Alcohol can pass directly into the bloodstream. The absorption rate depends principally on the concentration of the drug in the stomach and small intestine. This concentration is limited by the presence of alcohol dehydrogenase. Because women normally carry less alcohol dehydrogenase in their intestines, they usually consume less alcohol than men before showing its effects.
Alcohol is not stored in the body or excreted but is metabolized in the liver at a fixed rate of between 0.25 and 0.33 oz (7.1–9.4 grams) per hour, varying with the individual. Thus alcohol is found in the bloodstream and signs of intoxication appear when the rate of alcohol consumption is greater than the rate at which it is metabolized in the liver. At a blood level of about .05%, alcohol impairs concentration, visual function, psychomotor performance, and reaction time. For many years the legal standard for drunkenness in most states was a blood alcohol level of .10%, but in many states it now is .08%. The lethal level, often given as .60%, may be as low as .40% in some people. Blood alcohol concentrations are measured by breath (the Breathalyzer test), blood, or urine tests.
Alcohol abuse can result in broad range of medical problems. Alcohol can reduce production of the sex hormone testosterone in males, resulting in impotence and testicular atrophy. Alcohol has a high caloric value but a low nutritional value. Its "empty calories" may allow the alcoholic to feel satisfied while actually progressing toward a state of serious malnutrition. Ailments that can result from alcohol consumption include cirrhosis, a liver ailment; diseases of the digestive system; damage to the heart; lowered resistance to infection; and cancer (larynx, esophagus, liver). Women who consume alcohol during pregnancy are at risk of delivering children with fetal alcohol syndrome, a syndrome of physical, developmental, and psychological problems.
Although the medical effects of alcoholism have long been known, the study of how alcohol acts on the brain to produce intoxication, dependence, and tolerance is still new. Most studies focus on the effect of alcohol on cellular communication. These have found that different regions of the brain differ in their sensitivity to alcohol. In addition, alcohol affects many different kinds of receptors (see nervous system) and neurotransmitters, such as GABA, glutamate, and serotonin, creating different effects in each case. Whatever the exact mechanism, it is accepted that chronic consumption of alcohol results in disconnection of the fibers that connect brain cells, producing memory lapses, impaired learning ability, motor disturbances, and general disorientation. Two organic brain disorders, alcoholic dementia, characterized by general loss of intellectual abilities, and Wernicke-Korsakoff's syndrome, characterized by such symptoms as loss of physical coordination, incoherence, and mental confusion, are frequently seen in alcoholics.
Alcohol, like all addictive drugs, produces physical dependence in the habitual user. A hangover, a combination of headache, nausea, fatigue, and depression, may be a mild type of withdrawal from alcohol. Sudden abstinence by the chronic alcoholic produces a severe withdrawal syndrome—including tremors, vomiting, and convulsions resembling those of epilepsy—that is more likely to cause death than withdrawal from narcotic drugs. The final and most dangerous phase in this withdrawal pattern is delirium tremens, a toxic psychosis characterized by insomnia, hallucinations, seizures, and maniacal behavior.