Many people who are charged with DUI (driving under the influence) come to me and say I felt fine, I know I wasn’t slurring my words, I was driving the speed limit, etc. Yet, a cop pulled them over for whatever reason (could be something as simple as a broken tail light) and the officer suspected an impaired driver and arrested him or her.
The example I just set forth above is common. I don’t believe they are lying. They truly believe they weren’t drunk at the time of the stop ie. they were functioning at a high level. But what they fail to realize is that tolerance for alcohol doesn’t equate with sobriety or passing a blood alcohol test (BAC). One’s blood alcohol is not determined by tolerance for alcohol. Someone who regularly drinks a quart of vodka a day may have learned to function but that doesn’t mean that that person could pass a BAC test.
Others will tell me, “well, I was just drinking beer.” While beer has a lower alcohol content than hard liquor a standard drink of a 12-oz can of beer, a 1 ½ oz “shot” of 80-proof distilled spirits, or a 5-oz glass of wine all contain the same amount of pure alcohol, 13.7 gr (0.6 oz). The total amount of alcohol consumed, plus other moderating factors, not the type of alcoholic drink, determines the blood alcohol concentration (BAC).
The National Institute on Alcohol Abuse and Alcoholism estimates that consuming five or more drinks in about two hours (four or more drinks for adult females) brings the BAC to 0.08% or above, the legal limit for driving in all 50 states.
Several factors moderate the absorption, distribution, and metabolism of beverage alcohol. The presence of food in the stomach slows absorption. Drinking slowly and drinking more diluted alcohol allows the body to metabolize it while at the same time absorbing an incoming dose. Most people eliminate about one drink each hour from their system. An enzyme produced in the stomach, glutathione-dependent formaldehyde dehydrogenase, breaks down alcohol, decreasing its bioavailability. Alcohol is distributed in tissues according to water content. A person’s weight and sex determine the total volume of body water and, therefore, the BAC after drinking a certain amount of alcohol. In general, the more a person weighs, the larger the volume of body water and the lower the BAC. Alcohol pharmaco-kinetics differ by gender. Women have lower glutathione-dependent formaldehyde dehydrogenase activity, leading to increased alcohol absorption. They also generally have a higher fat content and less total body water, where ethanol is distributed. This contributes to higher BACs, an enhanced rate of alcohol oxidation in the liver, a slower rate of gastric emptying of alcohol, and higher vulnerability to the toxic effects of alcohol.5 But another phenomenon, “tolerance,” affects not only the BAC, but also the body’s capacity to cope with high levels of this toxic chemical.
Tolerance does affect a person’s ability to function and can fool someone into thinking that “I’m ok to drive” when they are actually drunk. In effect, drink for drink, a regular heavy drinker feels less drunk and may have less alcohol-induced impairment in speech, gait, and fine and gross coordination than his light-drinking counterparts. The biologic mechanisms of tolerance are complex. Different forms of tolerance have different mechanisms of action. Far from being a simple homeostatic response to the presence of alcohol in the brain, tolerance can develop within various time frames. Acute tolerance, also called “tachyphylaxis,” happens within a single drinking episode. In acute tolerance, signs of intoxication at the same BAC are more pronounced on the ascending than the descending portion of the BAC curve. Most experienced drinkers develop some form of acquired or chronic tolerance. Chronic tolerance is a bodily adaptation that makes a person need to drink more and more alcohol to get the same effect, or inversely, an adaptation that causes less and less response to a recurring dose.
Tolerance reduces the visible signs of intoxication. This makes it hard for others, including friends, alcohol servers, and law enforcement officers, to determine the drinker’s level of driving impairment. Those who experience tolerance commonly believe that since they can “hold” their alcohol, they are capable of driving safely after drinking. But alcohol reduces the physical and mental dexterity required for safe driving. Studies have determined that the risk of causing a crash rises proportionally with BAC. Even at lower BACs (0.05% to 0.09%), the likelihood of a crash is at least nine times greater than at zero BAC. At very high BACs (at or above 0.15%), the risk of crashing is 300 to 600 times the risk at zero or near-zero BACs.
So, just because you think you can handle your liquor, if you drink and drive, you are a candidate for a DUI.