A blood alcohol concentration (BAC) of 0.08% is the legal limit for driving in all 50 U.S. states, but a BAC is generally considered “high” in medical terms once it reaches 0.15% to 0.20% or above, where serious physical impairment, vomiting, and blackouts become likely. Above 0.30%, alcohol poisoning can be life-threatening. Understanding what these numbers actually mean for your body helps put the risk into perspective.
What BAC Measures
BAC is the percentage of alcohol in your bloodstream by volume. A BAC of 0.10% means there is one part alcohol for every 1,000 parts of blood. The number starts climbing within minutes of your first drink and peaks roughly 30 to 90 minutes after your last one, depending on how fast you drank and whether you ate beforehand.
In the United States, one standard drink contains 0.6 ounces (14 grams) of pure alcohol. That’s 12 ounces of regular beer at 5% alcohol, 5 ounces of wine at 12%, or a 1.5-ounce shot of 80-proof liquor. Many cocktails and craft beers contain significantly more alcohol than a single standard drink, which makes it easy to underestimate how much you’ve actually consumed.
How Impairment Builds at Each Level
Alcohol doesn’t flip a switch. Its effects accumulate gradually, and each jump in BAC brings measurably worse coordination, judgment, and reaction time.
0.02%: This is roughly one drink for most people. You may feel slightly relaxed with a mild mood shift. Your ability to track moving objects and divide your attention between two tasks already starts to decline, even though you feel mostly normal.
0.05%: Behavior becomes exaggerated, inhibitions drop, and alertness falls. Fine motor control starts slipping, like the ability to focus your eyes precisely. Steering a vehicle and responding to sudden hazards on the road become noticeably harder.
0.08%: The legal driving limit. At this point, muscle coordination is measurably poor across balance, speech, vision, reaction time, and hearing. Judgment, self-control, reasoning, and short-term memory are all impaired. You process information more slowly and have a harder time detecting danger.
0.10%: Reaction time and motor control clearly deteriorate. Speech is slurred, thinking slows, and maintaining a lane or braking at the right time while driving becomes very difficult.
0.15%: This is where most medical sources begin using the word “high.” Muscle control is far below normal, balance is significantly compromised, and vomiting often occurs unless tolerance has built up over time. Driving at this level involves substantial impairment in vehicle control, visual processing, and attention.
Where the Danger Zone Starts
Once BAC climbs above 0.15%, the risks shift from impaired judgment to genuine medical danger.
Between 0.16% and 0.30%, you may experience blackouts (gaps in memory where you remain conscious but can’t form new memories), repeated vomiting, confusion, and drowsiness so heavy it becomes difficult to stay awake. Losing consciousness in this range is common, and vomiting while unconscious creates a serious choking risk.
Above 0.30%, alcohol poisoning becomes likely. At this level, the brain’s ability to regulate basic survival functions starts to fail. Breathing may slow to fewer than eight breaths per minute or stop for stretches of 10 seconds or more. Body temperature can drop dangerously low. Loss of consciousness, coma, and death are all real possibilities in the 0.30% to 0.40% range.
Signs of Alcohol Poisoning
You won’t have a breathalyzer handy in most real-world situations, so recognizing the physical signs matters more than knowing the exact number. The warning signs that someone has crossed into a medical emergency include:
- Confusion or inability to respond coherently
- Vomiting, especially while semiconscious or unconscious
- Seizures
- Breathing that is very slow, irregular, or has long pauses
- Skin that looks blue, gray, or unusually pale
- Low body temperature (skin feels cold and clammy)
- Inability to stay conscious or be woken up
Binge drinking is the most common cause. For men, that means roughly five or more drinks within two hours; for women, four or more in the same window. Because BAC continues to rise after you stop drinking (alcohol in your stomach is still being absorbed), someone can seem “just drunk” and then deteriorate significantly 20 or 30 minutes later.
How Fast Your Body Clears Alcohol
Your liver processes alcohol at a fixed rate of about 0.015% BAC per hour. That rate holds regardless of your size, sex, or how much coffee you drink. Nothing speeds it up: not food, not water, not sleep, not exercise.
To put that in practical terms, if your BAC peaks at 0.15%, it would take roughly 10 hours for your body to return to 0.00%. A peak of 0.30% would take about 20 hours. This is why people can still be legally impaired the morning after heavy drinking, even if they feel relatively sober.
Why the Same Drinks Hit People Differently
Two people can drink the same amount and reach very different BAC levels. Body weight is the biggest factor: a smaller person has less blood volume, so the same amount of alcohol creates a higher concentration. Body composition matters too, because alcohol dissolves in water but not in fat. People with a higher percentage of body fat (and therefore less body water) will reach a higher BAC from the same number of drinks.
Biological sex plays a role partly for this reason. Women on average have a higher ratio of body fat to water than men of the same weight, which tends to produce a higher BAC per drink. Hormonal cycles, medications, and how recently you’ve eaten also shift the curve. Drinking on an empty stomach lets alcohol absorb much faster, producing a higher and earlier peak.
Tolerance is a separate issue entirely. Someone who drinks frequently may feel less impaired at a given BAC, but their coordination, reaction time, and organ exposure to alcohol are just as affected. Feeling “fine” at 0.15% doesn’t mean your body is handling it well.
What Happens at the Hospital
Treatment for severe alcohol intoxication is mostly supportive. There is no antidote that neutralizes alcohol. In an emergency room, the focus is on keeping the airway clear, monitoring breathing, maintaining body temperature, and preventing choking if vomiting occurs. Patients are typically observed until they are no longer clinically intoxicated and can be safely discharged. In extreme cases with very high BAC levels, dialysis may be considered to speed alcohol removal from the blood, though this is rare and comes with its own risks.