A blood alcohol concentration (BAC) of 0.30% or higher is generally considered life-threatening, and levels above 0.40% can be fatal. But dangerous impairment starts well before that. Even a BAC of 0.15% can cause vomiting, significant loss of balance, and serious risk of injury, while the 0.30% to 0.40% range is where alcohol poisoning, loss of consciousness, and death become real possibilities.
BAC is measured as a percentage of alcohol in your blood. Understanding what happens at each level helps you recognize when someone has crossed from “drunk” into a medical emergency.
What Happens at Each BAC Level
At 0.02%, the effects are subtle: slight relaxation, a mild mood shift, and a small decline in your ability to track moving objects. Most people feel fine and function normally at this level.
At 0.05%, judgment becomes noticeably impaired. You may feel loosened up and good, but coordination drops, alertness decreases, and your ability to respond quickly to unexpected situations is reduced.
At 0.08%, the legal driving limit in every U.S. state, muscle coordination is clearly affected. Balance, speech, vision, and reaction time all suffer. Reasoning, self-control, and short-term memory are impaired. This is the threshold the NIAAA uses to define binge drinking: reaching 0.08% typically requires about five drinks for men or four for women within two hours.
At 0.10%, deterioration is obvious. Speech slurs, thinking slows, and reaction time drops significantly.
At 0.15%, you’re in genuinely risky territory. Muscle control is far below normal, balance is seriously compromised, and vomiting often occurs. This is the level where the risk of choking, falling, or other injury-related emergencies climbs sharply.
Where Alcohol Poisoning Begins
Between 0.15% and 0.30%, confusion, drowsiness, and repeated vomiting set in. A person in this range may struggle to stay awake or respond coherently. The body is being overwhelmed faster than it can process the alcohol.
Between 0.30% and 0.40%, alcohol poisoning is likely. Loss of consciousness is common, and the body’s protective reflexes start shutting down. The gag reflex, which normally prevents you from choking on vomit, can stop working entirely. Breathing slows dangerously, heart rate drops, and body temperature falls.
Above 0.40% is considered potentially fatal for most people. A study of 98 deaths from accidental alcohol poisoning found that the average blood alcohol level at death was approximately 0.46% in cases without other contributing factors. When other drugs were involved, particularly sedatives or other psychotropic medications, the lethal level dropped to around 0.31%. That’s a critical point: mixing alcohol with other substances dramatically lowers the threshold for a fatal outcome.
How Alcohol Becomes Fatal
Alcohol kills through a few specific mechanisms, not just by being “too much.” At high concentrations, it suppresses the brainstem, which controls automatic functions like breathing. Breathing can slow to fewer than eight breaths per minute or stop for 10 seconds or more between breaths. If oxygen delivery to the brain and organs drops far enough, death follows.
Choking on vomit is another common cause of death. When a deeply intoxicated person vomits while unconscious and has no functioning gag reflex, vomit enters the lungs. This can cause suffocation or trigger a severe inflammatory lung reaction. Chronic alcohol use carries a two to three times greater risk of this type of acute respiratory failure, but even a single episode of extreme intoxication can cause it.
Dangerously low body temperature is a third risk. Alcohol dilates blood vessels near the skin, which makes you feel warm while actually accelerating heat loss. In cold environments, an unconscious person with a high BAC can develop fatal hypothermia.
Why the Same Number of Drinks Hits People Differently
BAC after a given number of drinks varies substantially from person to person. Body size and weight are the most obvious factors: a smaller person reaches a higher BAC from the same amount of alcohol. Body composition matters too, because alcohol distributes through water in the body. People with more muscle mass and less body fat have proportionally more water to dilute the alcohol, resulting in a lower BAC.
Women generally reach higher blood alcohol levels than men after drinking the same amount, even when body weight is similar. This is because women on average have less body water, more body fat, and hormonal differences that affect how quickly alcohol is absorbed and processed.
Whether you’ve eaten recently also makes a significant difference. Food in the stomach slows the rate at which alcohol enters the bloodstream. Drinking on an empty stomach can produce a BAC spike that’s substantially higher and faster than the same drinks consumed with a meal.
How Fast Your Body Clears Alcohol
The average person metabolizes about 7 grams of alcohol per hour, roughly equivalent to one standard drink. That translates to a BAC reduction of about 0.015% per hour for most people. This rate is relatively fixed. Coffee, cold showers, and food do not speed it up once alcohol is already in the bloodstream.
This means that someone who reaches a BAC of 0.30% would need approximately 20 hours for their body to fully clear the alcohol, assuming no more drinking. Even after waking up and feeling better, a person can still have a dangerously elevated BAC for many hours.
Signs That Someone Needs Emergency Help
The critical warning signs of alcohol overdose, as identified by the NIAAA, are:
- Mental confusion or stupor
- Inability to stay conscious or inability to be woken up
- Vomiting (especially while semiconscious or unconscious)
- Seizures
- Slow breathing: fewer than 8 breaths per minute
- Irregular breathing: gaps of 10 seconds or more between breaths
- Slow heart rate
- Clammy skin, bluish skin color, or paleness
- Extremely low body temperature
A person does not need to show all of these signs to be in danger. Someone who has passed out from drinking and cannot be woken up is in a medical emergency, even if their breathing appears normal at that moment. BAC can continue rising after a person stops drinking, because alcohol in the stomach and intestines is still being absorbed. A person who seems to be “sleeping it off” can deteriorate rapidly.