The potency of alcoholic beverages is measured by the percent of absolute alcohol they contain. Pure ethyl alcohol is 100 percent absolute alcohol. Beer contains about 4 or 5 percent. Wine is about 12 percent; it is the most potent drink we can concoct through the natural fermentation process. ("Fortified" wine, in which alcohol is added to the natural substance, by law may be no higher than 20 percent alcohol.

The wines skid-row alcoholics drink are usually "fortified." Sherry is a wine fortified with brandy.) However, the process of distillation (boiling, condensing, and recovering the more volatile, alcohol-potent vapor from the original fluid, and adding an appropriate proportion of water) produces drinks, like Scotch, vodka, gin, rum, and tequila, that are about 40 to 50 percent alcohol, or 80 to 100 "proof." Consequently, in order to consume roughly an ounce of absolute alcohol, someone would have to drink two 12-ounce cans of beer, or one 8-ounce glass of wine, or a mixed drink containing about 2V ounces of Scotch or gin. According to the rule of equivalency—which states that the effects of alcohol are determined mainly by the volume of absolute alcohol that is drunk, rather than the type of drink itself—these drinks would be roughly equal in strength, and would have approximately the same effects on one's body.

Alcohol, when it enters the body, is translated into what pharmacologists call blood-alcohol concentration (BAC), or blood-alcohol level (BAL). This corresponds fairly closely to the percent of one's blood that is made up of alcohol after it is ingested. There is a relationship between blood-alcohol concentration and what we do under the influence. The effects of alcohol are, to a large degree, dose-related: the more that is drunk, the greater the effect it has. There are, of course, person-to-person variations in this respect. And there are many qualifications that must be noted.

The effects of alcohol are influenced by many factors. Some of them are directly physiological. Since alcohol registers its impact via the bloodstream, the size of the drinker influences blood-alcohol concentration; the larger the drinker, the more alcohol it takes to make him or her drunk. The presence of food and water in the stomach will retard and space out over time—by as much as two times—the rate of absorption of alcohol into the bloodstream. Consequently, the less one has in one's stomach, the less it takes to bet one drunk. The faster one drinks, the less able the body is to metabolize die alcohol within a standard period of time, and the drunker one will become. One can drink small quantities of alcohol continually without demonstrating any effects at all, if the drinks are taken slowly enough. The presence of carbonation in an alcoholic beverage—as, for example, in cham pagne or sparkling Burgundy—will speed up the metabolism process and can make one drunker more quickly.

As with practically all drugs, alcohol builds pharmacological tolerance: It takes more to have an effect on a regular drinker than on an abstainer, more on a heavy drinker than an infrequent drinker. Much of this is behavioral tolerance: simply learning to get used to alcohol's effects. But biochemical tolerance does develop as well. There is a kind of "plateau," however: It requires something like twice as much alcohol to have an effect in the sensorimotor realm in the heavy, long-term drinker as in the moderate drinker.

Alcohol's strictly physiological effects include cellular dehydration (a major reason for a hangover the day after), gastric irritation (which may lead to an upset stomach after drinking too much), vasodilation (an increase of blood flow through the capillaries), a lowering of body temperature (though the surface of the skin does become flushed, creating an illusion of greater body warmth), some anesthesia, and a depression of many functions and activities of the organs of the body, especially the central nervous system. Alcohol also disorganizes and impairs the ability of the brain to process and use information.

One ounce of alcohol consumed in less than an hour will result in a blood-alcohol concentration of roughly .05 percent in a person of average size (see Table 5.1). This produces in most people a mild euphoria, a diminution of anxiety, fear, and tension, a corresponding increase in self confidence and, usually, what is called a "release" of inhibitions (an effect I'll have to qualify shortly). Decreased fear also typically results in a greater willingness to take risks; this effect has been demonstrated in laboratory animals . Alcohol is, for most people, at low doses, a mild sedative and a tranquilizer. This is by no means universally the case, however. There are many people for whom alcohol ingestion results in paranoia, distrust, heightened anxiety, and even hostil ity. These "effects," however, typically occur, when they do, at high doses. And at low doses, alcohol will result in little or no diminution of motor and intellectual performance.

Alcohol's effects on motor performance are familiar to us all: clumsiness; an unsteady gait; an inability to stand or walk straight; slurred speech. One's accuracy and consistency in performing mechanical activities decline dramatically as blood-alcohol concentration increases. And the more complex, the more abstract, and the more unfamiliar the task, the sharper the decline. The most noteworthy example is the ability to drive an automobile. It is crystal clear that drinking, even moderately, deteriorates the ability to drive, and contributes to highway fatalities.

How intoxicated does one have to be to lose the ability to perform mechanical tasks? What does one's blood-alcohol level have to be to display a significant decline in motor coordination? And how many drinks does this represent? The answers depend on a number of factors, as I just said, experience with alcohol being crucial. It is true that seasoned drinkers can handle themselves better at the same blood-alcohol level than novices can, but experienced drinkers are typically far too overconfident about their ability to function while under the influence. In fact, since alcohol tends to dull anxiety and tension, drunk drivers typically think that they perform better than they actually do—and are surprised, even incredulous, when their ineptitude is demonstrated to them—so that the problem becomes more than a simple deterioration in mechanical ability. All drinkers experience a loss of motor skills at a certain point, and it occurs at a fairly low BAC. However, many drivers are quite willing to get behind the wheel while intoxicated: In 1986 in the United States, there were 1.8 million arrests for drunk driving.

There is a kind of "zone" within which alcohol impairment occurs. At about the .03 percent blood-alcohol level, some very inexperienced and particularly susceptible individuals will display significant negative changes :n the ability to perform a wide range of tasks. (See Table 5.1 for an indication of how much alcohol this entails for a 150-pound person.) The Federal Aviation Administration (FAA) sets a .04 percent BAC as representing an alcohol-influenced condition, and prohibits pilots from flying at this level of intoxication. As we can see from Table 5.1, this is less than two typical drinks.

At the .10 level, even the most hardened, experienced, and resistant drinker will exhibit some impairment in coordination. Most states set a BAL of. 10 as constituting legal intoxication—a far too conservative a level, in the view of most experts. At the .04 percent level, for most people, there is no measurable increase in the likelihood of having a highway accident. But at the .06 percent level, the risk doubles. As we can see, this is only slightly more than two typical mixed drinks, or two beers, or two glasses of wine. At the .10 level, one's driving ability deteriorates by 15 percent, and one's .ikelihood of having an accident shoots up six or seven times, according to one estimate.

According to another estimate, at a .08 BAL, one's risk of being involved in a fatal car crash triples, and at .12, it increases fifteenfold . At the .15 level of bloodalcohol concentration, which constitutes "driving while intoxicated" (DWI) everywhere in the United States, one's skill at handling an automobile drops by one-third and one's chances of smashing up increase by between 10 to 50 times .

Motor-vehicle crashes are the most common cause of "non-natural" death in the United States; they account for more fatal injuries than any other type of accident. The proportion of drivers involved in fatal crashes whose BAL tested at .10 or higher was 50 percent in 1980. This figure declined through the 1980s to 38 percent in 1985 (Brooke, 1986), but in 1986, the number of deaths from drunk driving increased a bit (Stevens, 1987). Taking all traffic fatalities together—drivers, passengers, pedestrians, and cyclists—42 percent were alcohol-related in 1983. The National Highway Traffic Safety Administration reported that 60 percent of fatally injured drivers of motorcycles had a BAC of. 10 or higher; for fatally injured drivers of heavy trucks, this was only 20 percent. Even pedestrians vastly increase their chances of being killed by an automobile—more than fivefold!—if they are intoxicated. A third of pedestrian fatalities in one study had a BAC of .15 or higher, whereas only 6 percent of the control group randomly selected at the same time and place were this intoxicated .

Automobiles are not the only source of fatal alcohol-related accidents. The National Transportation and Safety Board estimates that nearly 70 percent of drownings are alcohol-related. The U.S. Coast Guard estimates that of all boating accidents that result in a drowning, 88 percent are alcohol-related. Nearly half (46 percent) of all burn victims had been using alcohol at the time of their injury. In roughly a quarter of all suicides . In an unpublished study supplied by the chief medical examiner of North Carolina, the following figures represent the percent of people who died of each cause who registered a BAC of .10 or higher: drowning, 41 percent; fire, 58 percent; stabbing, 68 percent; firearms, 40 percent. Another study examined a thousand consecutive violent or accidental deaths in New York City in 1972. A BAC of .10 or higher was found in a third of all victims—33 percent for victims of falls, 44 percent for vehicular drivers or passengers, and 32 percent for pedestrians (Haberman and Baden, 1974). Numerous studies (CombesOrme et al., 1983; Abel and Zeidenberg, 1985; Goodman et al., 1986) show that close to half of all homicide victims were drinking at the time they were killed, and one-third had a BAC of .10 or higher. Adding it all up, one estimate holds that in 1980 alone, alcohol was responsible for nearly 60,000 premature deaths from accident . Thus, in one year, alcohol was responsible for the loss of more American lives—not even counting the illnesses it caused—than was the Vietnam War.

Beyond the .15 blood-alcohol level, one's ability to function plummets. At the .20 level, the drinker is somewhat dazed, confused, and distinctly uncoordinated; any movement at all becomes risky and problematic. Driving is extremely hazardous. At the 30 level, any response to the stimuli of the outside world becomes an insurmountable chore. One's ability to perceive and comprehend what is happening is reduced to a bare minimum. At the .40 level, most people pass out and lose consciousness; this is regarded as the LD-50—the point at which half of all drinkers die from an overdose. At 50 percent, if the drinker is still alive, he or she has entered a coma, from which he or she can be aroused only with the greatest difficulty. At 60 percent, overdoses are increasingly common; death occurs as a result of the inhibition and paralysis of the respiratory centers. Almost anyone whose blood is 80 percent alcohol will die.