The question of how many drinks it takes to become intoxicated is common, but it lacks a single, universal answer. The physical state known as “drunk” is not determined by a simple count of glasses but by the concentration of alcohol that reaches the brain. This concentration varies wildly from person to person based on a complex interplay of physiology, consumption rate, and the actual amount of alcohol consumed in each drink.
What Constitutes a Standard Drink
In the United States, one standard drink is defined as containing approximately 0.6 ounces (14 grams) of pure ethanol. This amount of pure alcohol is consistent across different types of beverages, despite their varied serving sizes and alcohol concentrations.
A standard drink is equal to a 12-ounce serving of regular beer (about 5% alcohol by volume, or ABV). A 5-ounce glass of wine (generally around 12% ABV) also contains the same 0.6 ounces of pure alcohol. Similarly, a 1.5-ounce shot of distilled spirits, such as vodka or whiskey (40% ABV/80 proof), constitutes a single standard drink.
Defining Intoxication: Blood Alcohol Concentration (BAC)
Scientifically, intoxication is measured by Blood Alcohol Concentration (BAC), which is the percentage of alcohol present in the bloodstream. A BAC reading of 0.08%, for example, means that there are 0.08 grams of alcohol for every 100 milliliters of blood. The effects felt by an individual directly correspond to the rising percentage of alcohol in their blood.
At a BAC of approximately 0.02%, a person may feel a mild sense of relaxation. As the concentration rises to 0.05%, judgment becomes impaired, and alertness is lowered.
The legal limit for driving in most of the U.S. is 0.08% BAC, a level at which muscle coordination and reasoning are impaired. Reaching 0.10% often leads to slurred speech and slowed reaction time. A BAC of 0.15% results in significant loss of balance and muscle control, often accompanied by nausea.
Key Biological and Environmental Factors Influencing BAC
Two people consuming the exact same number of standard drinks at the same rate will almost always register different BACs due to various biological factors. Body weight is a significant variable because alcohol is distributed throughout the total body water. A person with less body mass has less water to dilute the alcohol, leading to a higher concentration in the bloodstream for the same amount consumed.
Biological sex also plays a role, as women typically achieve a higher BAC than men after consuming an equal amount of alcohol. This is partly because women generally have a lower percentage of body water and a higher percentage of body fat, which concentrates the alcohol more readily. Furthermore, women tend to have lower levels of the enzyme alcohol dehydrogenase, which begins to metabolize alcohol in the stomach before it enters the bloodstream.
The rate of consumption is another major determinant of the peak BAC level. Drinking quickly overwhelms the body’s immediate capacity to process the alcohol, causing the concentration in the blood to spike rapidly. The presence of food in the stomach can also slow the absorption of alcohol into the bloodstream by obstructing its passage, which delays and lowers the peak BAC achieved.
Estimating Impairment and Rate of Alcohol Elimination
The liver begins the process of metabolism to eliminate alcohol from the body. This elimination occurs at a relatively constant and predictable rate, averaging about 0.015% BAC reduction per hour for most people. This rate is fixed and cannot be sped up by consuming coffee, taking a cold shower, or exercising.
This metabolic rate means it takes approximately one hour for the body to process the amount of alcohol found in one standard drink. Time is the only factor that reduces the alcohol concentration in the blood, emphasizing the need for planning to ensure sobriety.