How long alcohol is detectable in the body (in the blood, in the saliva/on the breath, or in urine) depends on several factors.
Drinking sessions often last for an hour or more, sometimes going on for several hours. However, being rapidly metabolized, alcohol in the bloodstream quickly disappears in relatively short order (usually within several hours) after the last drink, even after a lengthy drinking session.
Although alcohol passes through the digestive system, it requires little to no actual digestion. Once consumed, 20 percent of the substance moves directly from the upper gastrointestinal tract into the bloodstream, where it is carried throughout the body and travels to the brain. The rest enters the bloodstream somewhat more slowly after being absorbed by the small intestines. This process may be somewhat slowed when there’s food in the stomach and intestines, which may slightly delay the onset of intoxication.
As alcohol circulates through the bloodstream, the liver begins to break it down via a sequence of metabolic processes. Despite the fact that people get intoxicated from alcohol at different rates and from different amounts of the substance, a healthy liver will generally metabolize the substance at a fairly uniform rate regardless of sex, race, or weight. Despite this generally uniform rate, metabolization in the liver is not the only factor that determines how fast alcohol leaves the body. Other factors that may influence the windows of alcohol detection in the body include:
On average, the liver can metabolize 1 ounce of alcohol every hour. The average person’s blood alcohol level from a single ounce of alcohol will rise to 0.015, and about every hour, that much alcohol will be cleared from a person’s body. The amount of alcohol required to achieve a blood alcohol limit of 0.08, the legal limit for driving, will take approximately 5.5 hours to be completely cleared from the system.
Once the blood alcohol level rises above 0.055, some people may begin to experience certain unpleasant effects, including depressed mood, irritability, nausea, vomiting, disorientation, and memory loss.
The time window for detection with many standard assays for urine alcohol is within 12 hours or less after the last drink. Relatively newer screening measures test for the presence of alcohol metabolites (ethyl glucuronide or ethyl sulfate) for as long as 5 to 7 days after the last drink. These more sensitive tests can be somewhat problematic, as they could report a false positive after an individual has come into contact with products such as alcohol hand sanitizers or mouthwashes.
Like most substances, alcohol can be detected in a person’s hair for around 90 days after being last consumed. It can also be detected via saliva swab, which can find traces of alcohol 12-24 hours later.
According to the National Survey on Drug Use and Health, roughly 15.1 million people age 12 or older had an alcohol use disorder in the US in 2016. This figure represents 5.6% of all people in this age group. Alcohol-related deaths are the third leading causes of preventable death in the country, with 88,000 people dying each year from things like liver failure, overdose, drunk driving, and other accidents.
Knowing more about how alcohol is metabolized and keeping track of one’s likely blood alcohol levels can help to prevent unintended over-intoxication and accidental death from alcohol poisoning. It can also help someone to avoid a cycle of growing tolerance, increased drinking to overcome tolerance, physical dependence and, ultimately, a compulsive pattern of problematic alcohol use that culminates in addiction development.