The definition of “drunk,” or intoxication, describes a state where alcohol consumption has altered a person’s physical and mental functioning. This condition causes temporary changes in mood, coordination, judgment, and reaction time. Determining this state relies on precise, measurable physiological standards rather than subjective feelings. Scientific and legal definitions are based on the concentration of alcohol absorbed into the bloodstream.
The Scientific Standard: Blood Alcohol Concentration (BAC)
The universally accepted scientific metric for intoxication is Blood Alcohol Concentration (BAC), which measures the percentage of alcohol present in the bloodstream. BAC is expressed as a percentage, where 0.08% indicates 0.08 grams of alcohol per 100 milliliters of blood. Alcohol is rapidly absorbed through the stomach and small intestine before being distributed throughout the body’s water content.
Professionals determine BAC using several methods. A direct blood draw provides the most accurate reading, while a breathalyzer estimates BAC by measuring alcohol content in exhaled air. The breath measurement relies on a ratio correlating breath alcohol with blood concentration. Since the liver metabolizes alcohol at a fixed rate, consumption exceeding this pace causes the BAC to rise, increasing intoxication.
Legal Thresholds for Impairment
Legal systems use BAC measurements to establish boundaries for driving and public safety. The common legal limit for operating a motor vehicle in the United States is 0.08% BAC for drivers over 21. Exceeding this threshold constitutes being “legally intoxicated” and results in penalties, even if a driver shows no obvious physical signs of impairment.
A person can still be considered impaired at lower concentrations, and most states allow for arrests based on visible signs of reduced ability even if the BAC is below 0.08%. Stricter limits are often applied to specific populations to maintain higher safety standards. For instance, many jurisdictions enforce a zero-tolerance policy for minors, setting the limit as low as 0.01% or 0.02%. Commercial drivers also face a lower standard, typically 0.04%.
Observable Signs of Intoxication
The effects of intoxication progress in predictable stages as the BAC rises. At a low BAC, around 0.02%, a person may feel relaxed and experience subtle deficits in judgment. As the concentration moves closer to 0.05%, euphoria increases, accompanied by lowered alertness and reduced muscle control.
Once a person reaches 0.08%, noticeable impairment includes reduced coordination, slurred speech, and slower reaction time. In the range of 0.10% to 0.15%, individuals experience significant reduction in motor function, difficulty balancing, and potential nausea. At very high concentrations, such as 0.20% and above, confusion, disorientation, and a risk of blackout or loss of consciousness become likely.
Factors Determining Individual Intoxication Levels
The rate at which a person becomes intoxicated varies significantly because the same amount of alcohol does not produce the same BAC in everyone. Body weight is a major factor, as individuals with greater body mass have more water to dilute the alcohol, resulting in a lower peak BAC. Biological sex also plays a role because females generally have a higher percentage of body fat and less body water than males, which leads to a higher concentration of alcohol in the bloodstream.
Food and Consumption Rate
The presence of food in the stomach slows the absorption of alcohol into the bloodstream by keeping it in the stomach longer. Drinking on an empty stomach therefore leads to a quicker and higher spike in BAC. The speed of consumption also directly influences the level of intoxication; rapid consumption overwhelms the liver’s ability to metabolize the alcohol, causing a sharp rise in BAC.
Other Influences
Other influences include the use of certain medications, which can amplify the effects of alcohol. Genetic variations in the enzymes responsible for breaking down alcohol also affect individual BAC levels.