Blood Alcohol Concentration: What to Know About Alcohol Levels
Key takeaways:
Blood alcohol concentration (BAC) measures the alcohol level in your bloodstream.
Many factors affect the rise and fall of BAC — beyond how much alcohol you drink and how fast you drink it. Sex, weight, and the timing of your last meal can affect BAC.
Your BAC does not always reflect how intoxicated you act or feel. So there’s no set alcohol level that corresponds to alcohol poisoning.
Blood alcohol concentration (BAC) — also known as blood alcohol level — is a measure of how much alcohol you have in your blood. How much you drink plays a role, but other things affect BAC, too. It’s also determined by how you metabolize alcohol, which can be affected by a number of different factors.
To make matters more confusing, BAC does not always correspond to the level of intoxication. Someone with a low BAC may be significantly impaired, whereas someone with a high BAC may seem barely affected. So understanding BAC can help you learn how to keep yourself and others safe when drinking.
Read on to learn more about how your blood alcohol level is measured, what factors affect it, and what it means from a health perspective.
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How is blood alcohol concentration measured?
A blood test is the best way to determine BAC. Some people purchase a Breathalyzer to figure out their BAC. But these devices aren’t always accurate. There are also over-the-counter saliva and urine tests for alcohol levels. But these tests do not accurately measure alcohol concentrations either.
There are also some online tools that can help you get a rough estimate of your BAC. This online calculator estimates your BAC using your sex, weight, how many drinks you’ve had, and over what period of time. You might be surprised at your BAC after just 1 drink.
What factors affect blood alcohol levels in your body?
Different factors can influence how you metabolize alcohol. And this can affect your BAC. Some of these factors are based on choice and some are based on biology:
Sex: In general, the female body tends to have more fat and less water than a male body of the same weight. This means that alcohol is more concentrated in a female body, so BAC will rise quicker.
Weight: Similar to sex, weight affects how much water someone has in their body. The lower someone’s weight, the less water in their body to absorb the alcohol. So their BAC will rise faster.
Age: The body processes alcohol differently as you age. This is in part due to a change in body composition, similar to sex and weight above. The liver may also become less efficient at metabolizing alcohol. And older adults are more likely to take medications that can affect BAC.
Medications: Many medications interact with alcohol and can change how you metabolize alcohol — and vice versa. This includes antibiotics, antidepressants, antihistamines, and medications for pain, anxiety, or sleep. Some of these may increase your BAC.
Your last meal: If you drink on any empty stomach, alcohol gets absorbed faster into the bloodstream and can spike your BAC much quicker. When there’s food in your stomach, it slows down this absorption and leads to a slower rise in BAC.
What you drink: Not all drinks have the same amount of alcohol. For example, a 5 oz glass of wine has the equivalent amount of alcohol as a 12 oz beer or 1.5 oz shot of tequila.
How fast you drink: Drinking alcohol quickly will also make your BAC rise accordingly.
How does blood alcohol concentration correlate to intoxication level?
Everyone is different in how intoxicated they feel at different blood alcohol levels. The effects of alcohol on your body begin with your first drink, whether you feel it or not. This table outlines the typical side effects you can expect from alcohol as your BAC rises.
BAC | Typical effects |
0.02% | The level where people often feel “buzzed” Relaxed and mildly disinhibited Altered decision-making |
0.05% | Less coordinated Trouble with focusing eyes Less alert Slower response time |
0.08% | Trouble with speech Poor balance Difficulty remembering things Poor judgment If you tried to drive, you would have trouble maintaining speed, recognizing traffic signs, dangers in the road, etc. |
0.10% | Significantly slurred speech Poor coordination If you tried to drive, you would have trouble staying in your lane and braking at the right time |
0.15% | Difficulty staying balanced Possible vomiting Possible loss of consciousness |
How quickly you reach these BAC levels — and how you feel at each one — will depend on many of the factors we discussed above. So it’s always a good idea to assign a designated driver who can drive sober. It’s illegal to drive if you have a BAC of 0.08% or higher. But as the table shows, the effects of lower blood alcohol levels can lead to poor decision-making.
How do you lower your blood alcohol concentration?
You can’t speed up your body’s natural detoxification process or change how long alcohol stays in your system. While the effects of alcohol may start to wear off after 1 hour, your blood levels may take up to 6 hours to normalize. And it can take up to 24 hours before you fully metabolize all the alcohol in your body.
There are many myths on how to sober up fast, like drinking coffee or eating foods with lots of carbohydrates. While these things may help you feel a little better, they won’t change the rate at which your body metabolizes alcohol. And your decision-making skills and reflexes won’t return to normal until your BAC goes back down.
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What level of blood alcohol concentration is too high?
There’s no clear BAC level that determines when someone has a life-threatening amount of alcohol in their blood. But as a general guideline, a BAC of 0.31% or above is considered life-threatening. A BAC above 0.40% is a medical emergency, even if there are no severe signs of alcohol poisoning.
What level of blood alcohol concentration is considered alcohol poisoning?
Alcohol poisoning, or alcohol overdose, is a life-threatening condition. It occurs when BAC is so high that brain function is significantly impaired. And this can affect more than your level of consciousness — it can affect things like breathing and heart rate.
Signs of alcohol overdose can include:
Confusion
Vomiting
Slow breathing (fewer than 8 breaths a minute)
Abnormal breathing, such as long pauses between breaths
Cold body temperature
Blue or pale skin
Extreme drowsiness
Loss of consciousness
Going to sleep or passing out with a high BAC can be especially dangerous. Your blood alcohol level can continue to rise while you’re unconscious and unable to call for help. So if you’re worried that your or someone else’s blood alcohol level is too high, call 911 for help right away.
The bottom line
It helps to understand the different things that can affect your blood alcohol concentration (BAC). This way, you can take measures to stay safe when you’re drinking. Keep in mind that any rise in BAC can be dangerous. So, at the end of the day, the exact number is less important. If you or someone near you seems to be too intoxicated, it doesn’t matter how many drinks are in their system. Call 911 for help.
Why trust our experts?
If you or someone you know struggles with substance use, help is available. Call SAMHSA’s National Helpline at 1-800-662-HELP (4357) to learn about resources in your area.
References
Centers for Disease Control and Prevention. (n.d.). Blood alcohol concentration (BAC).
Department of Drug and Alcohol Programs. (n.d.). Alcohol poisoning or overdose. Commonwealth of Pennsylvania.
MedlinePlus. (2020). Blood alcohol level.
National Institute on Alcohol Abuse and Alcoholism. (2021). Understanding the dangers of alcohol overdose.
National Institute on Alcohol Abuse and Alcoholism. (n.d.). Core resource on alcohol.
NI Direct. (n.d.). What happens when you drink alcohol.
Paton, A. (2005). Alcohol in the body. BMJ.
