Your blood alcohol concentration (BAC) determines how intoxicated you get from drinking alcohol and varies by your sex and body weight. Also known as blood alcohol content, BAC is used for both legal and medical purposes.
In the United States, a BAC of 0.10 (one-tenth of one percent) means that there is 0.10 g of alcohol for every 100 milliliters (mL) of blood. According to law, the legal limit for operating a motor vehicle is 0.08 for drivers 21 and older. Many states have zero-tolerance policies for drivers under the legal drinking age, making it illegal to have a BAC over .00 if you are under 21.
Blood alcohol concentration can differ significantly between men and women, with women tending to have higher BAC than men of the same age and weight. This difference is due to several factors, including the amount of body water, body fat, and the activity level of alcohol dehydrogenase (ADH), an enzyme that breaks down alcohol in the liver.
Even though men have higher levels of ADH than women, it does not mean that they can drink more alcohol without getting intoxicated. Because men typically weigh more than women, they can have a higher BAC after consuming the same amount of alcohol.
One drink equals 1 12-ounce bottle of beer, 5 ounces of wine, or 1 oz of 100-proof spirits. Because men metabolize alcohol faster than women, a man would have to drink more than a woman to reach the same BAC.
Most people will tell you that one drink is "no big deal." While some men may respond to a single drink with tipsiness, others may appear unaffected. This does not mean that they've "cleared" the alcohol from the body; it simply means that their brains are more accustomed to alcohol and won't react as profoundly.
As a general rule, the average speed of metabolism (in which the alcohol is fully broken down and no longer present in the blood) will be slower the smaller a man is. The effects of drinking, therefore, can vary as can the speed by which the BAC returns to normal. For example:
After just one drink, it will take around two hours for the BAC to return to zero, even in larger men.
Two standard American drinks will, on average, produce a blood alcohol concentration of about 0.04, and most light and moderate drinkers will feel relaxed at this level. Even if you don't feel the effects of intoxication, your reaction times will be slowed and fine motor skills will be affected to the extent that driving will be impaired.
After two drinks, the metabolism of alcohol in men will further slow, meaning that you will have to wait longer before you get behind the wheel. For example:
After two drinks, it will take between four and six hours for your BAC to return to zero.
Three American standard drinks will produce, on average, a BAC of about 0.06. At this point, the negative effects of alcohol start to show.
Once the typical man has had three drinks, judgment will be impaired, often affecting the ability to make rational decisions, particularly around risk-taking activities such as driving or sex. Perception, memory, coordination, alertness, and self-control will also be impaired.
After a man has three standard drinks, the equation changes even further:
By the time you've consumed three drinks, you may already be well over the legal alcohol limit, especially if you weigh 150 pounds or less.
When the BAC reaches 0.12, vomiting is not uncommon, as it is the body’s first line of defense against alcohol poisoning.
The effects noted at the three-drink level (or a BAC of 0.06) will become more pronounced with each additional drink. Six drinks will produce a BAC of about 0.12 unless the alcohol consumed over a long period of time.
The speed by which a man would reach this level would vary:
After six drinks, the BAC and symptoms of severe intoxication and poisoning rapidly increase: