Final answer:
A person over 21 is considered intoxicated in the U.S. at a BAC of 0.08% or higher. This level accounts for average alcohol metabolism and is the legal threshold for activities requiring judgment, such as driving.
Step-by-step explanation:
In the United States, a person over the age of 21 is legally considered intoxicated with a blood alcohol concentration (BAC) of 0.08% or higher. This level of BAC has been established as the threshold for legal intoxication for the purpose of driving and other activities that require skill and judgment. It is also a point where acute intoxication can occur with symptoms such as decreased reaction time, visual acuity, and behavioral control.
The limit of 0.08% is not just a random figure; it takes into account the average rates at which the human body can metabolize alcohol, which is approximately 15 mg/dL per hour. However, the effects of alcohol can vary greatly between individuals, so it's important to drink responsibly and be aware of one's own limits.