Blood Alcohol Levels: Why They’re Important
Blood alcohol levels are a way of measuring how much alcohol is circulating in your body when you have been drinking. It is determined by how quickly alcohol is absorbed in the stomach, distributed throughout the bloodstream, metabolized in the liver, and eliminated as waste.
Alcohol diffuses across all cells and tissues in the body, including the brain. If you are consuming alcohol at a faster rate than your body can metabolize it, your blood alcohol level rises and you feel intoxicated.
In this article:
- How Are Blood Alcohol Levels Used?
- How Is Blood Alcohol Level Calculated?
- What Are Healthy and Unhealthy Blood Alcohol Levels?
- Importance of Blood Alcohol Levels in Understanding Alcohol Abuse and Addiction
- Short-term Effects of High Blood Alcohol Content
- Long-term Effects of High Blood Alcohol Levels
- Hope with Recovery
How Are Blood Alcohol Levels Used?
Your blood alcohol level is a better indicator of how intoxicated you are than the number of drinks you have consumed. The higher the blood alcohol level, the higher the degree of intoxication and impairment.
When you drink, your blood alcohol level is affected by many factors including:
- Your height and weight
- Your gender
- The speed of consumption
- Any other medications you might be taking
- Whether or not you have food in your stomach
- Type of alcoholic drink being consumed.
Most people can physically process about 1 alcoholic drink per hour, although the ability to metabolize alcohol varies greatly. For example, people with a long history of alcohol use, poor nutrition, smoking, and age lose the ability to metabolize alcohol safely and efficiently. Some genetic factors may also affect your body’s ability to metabolize alcohol. 1,2,3,4
Blood alcohol levels are important in evaluating the legal and physical effects of alcohol use. Blood alcohol levels are used to determine if you are:3,4,5
- Legally intoxicated while driving or when being disruptive in public
- Using alcohol while in a treatment program or while on probation or parole
- Too impaired to legally consent to sex
- At risk for alcohol poisoning, which can be fatal
The legal blood alcohol level is below .08% and it is illegal to drive in any state with a blood alcohol level greater than .08%. Results from a blood alcohol level test are usually interpreted as follows:4
- Sober: 0.0%
- Legally intoxicated: .08%
- Very impaired: .08–0.40%.
- Greater than .40% is considered a lethal blood alcohol level with a significant risk of acute alcohol poisoning, coma, or death.
How is a Blood Alcohol Level Calculated?
Blood alcohol levels are most accurately measured by a blood test. The breathalyzer is also a blood alcohol level calculator that measures the amount of alcohol in a driver’s breath, although it is not as accurate as a blood test.
The amount of alcohol in the bloodstream is measured in milligrams (mg) per 100 milliliters (ml) of blood. A blood alcohol level of .10 (0.1% or one-tenth of 1%) means that your blood contains one part of alcohol for every thousand parts of blood.
A blood alcohol test can accurately measure the amount of alcohol in your system up to 12 hours after you last drank alcohol. 3,4
What Are Healthy and Unhealthy Blood Alcohol Levels?
According to the Center for Disease Control and Prevention (CDC), the following people should not consume alcohol:
- Women who are pregnant or who might become pregnant
- Those under the legal age for drinking
- Those with certain medical conditions or who are taking medication that can interact with alcohol
- Those recovering from an alcohol use disorder and have difficulty controlling the alcohol consumption
Although drinking less or not at all is best for your health, drinking in moderation can reduce the health risks of consuming alcohol. Drinking in moderation is defined as limiting drinks to two or fewer per day for men and one or fewer per day for women.
Heavy and Binge Drinking (Problem Drinking)
Heavy drinking is defined as drinking:
- 15 or more drinks per week for men
- 8 or more drinks per week for women
Binge drinking is another form of problem drinking, which is defined as:
- 5 or more drinks at one time for men
- 4 or more drinks at a time for women
This is typically enough to bring your blood alcohol level up to 0.08% or more in approximately two hours. 1
A standard drink equivalent contains approximately 6 ounces of pure alcohol, which is contained in:
- 12 ounces of beer (5% alcohol content)
- 8 ounces of malt liquor (7% alcohol content)
- 5 ounces of wine (12% alcohol content)
- 5 ounces of 80-proof liquor (40% alcohol content) 1
Importance of Blood Alcohol Levels in Understanding Alcohol Abuse and Addiction?
As your body adapts to having alcohol in your system with chronic use, it begins to require more alcohol to get the same high and to tolerate increasing blood alcohol levels. Increased tolerance is one sign that an alcohol use disorder might be present.
Another sign is withdrawal symptoms when you stop drinking. Alcohol is a depressant and it slows down your central nervous system. To compensate for the effects of alcohol, your body has to work harder to function and to keep you focused.
Your blood alcohol drops severely when you suddenly stop drinking, but your brain keeps functioning in this overstressed state. This triggers withdrawal symptoms including:
- Shaking and tremors
- Nausea and vomiting
- Inability to sleep
In severe cases of withdrawal, seizures and hallucinations can occur for two or three days after you stop drinking. Withdrawing from alcohol can be life-threatening, but there are ways to help people detox safely and more comfortably. 7
Other signs that you might have an alcohol dependency or addiction include:1,7
- Difficulty controlling when and how much you drink
- Continuing to use alcohol even when there are problems at work or with friends and family
- Craving and thinking about alcohol all or most of the time
Short-term Effects of High Blood Alcohol Content
Alcohol passes from the blood to the brain and immediately causes changes in mood, thinking, coordination, alertness, and self-control.
The following list shows how standard drinks affect the blood alcohol level in an average male weighing 160 pounds and the effects on the brain and body: 4,5, 6
- 1-2 drinks: Blood alcohol levels can increase to 0.05%. This causes mild intoxication, relaxation, disinhibition, mild euphoria, decreased response time, and drowsiness.
- 3-4 drinks: Blood alcohol levels increase to between 0.05% to 0.10%. This causes moderate levels of intoxication. Fine motor skills and balance are impaired as well as judgment. Mood and self-control are altered. Visual perception and reflexes are impaired. Legal impairment occurs at 0.08% in all states.
- 5-7 drinks: Blood alcohol levels increase to between 0.10% to 0.15%. Moderate to high levels of intoxication result. Visual perception, reflexes, cognition, memory, and judgment are all impaired. Personality may change and people can become belligerent and aggressive.
- 8-10 drinks: Blood alcohol levels increase to between 0.15% to 0.30%. This causes severe intoxication. People are unable to walk or speak clearly, coordination is affected, and even standing may be difficult. Double vision or blurry vision is present. Vomiting and nausea are common.
- >10 drinks: Blood alcohol levels increase to 0.30% and above. Alcohol poisoning can occur and blood alcohol levels this high can be lethal. The person may lose consciousness or become comatose and be at risk of breathing or choking on vomit.
Research has shown that high blood alcohol levels can increase the risk of:3,6,9
- Motor vehicle accidents, occupational accidents, drowning, burns, and falls
- Dating and domestic partner violence, sexual assault, and homicide
- Violence, including homicide, suicide, sexual assault, and intimate partner violence
- Child abuse and neglect
- Risky sexual behaviors and increased risk of sexually transmitted diseases and unplanned pregnancy.
- Miscarriage, premature birth, stillbirth, and fetal alcohol spectrum disorders (FASD)
Long-term Effects of High Blood Alcohol Levels
Chronic drinking damages your brain, organs, and metabolism, and can even lead to death—approximately 95,000 people die each year from excessive alcohol use. Chronic alcohol misuse is responsible for about 10% of all deaths of working-age people (20-64) in the U.S. and accounts for nearly 11,000 traffic fatalities each year. 9, 5
Liver disease is among the most common medical problems associated with alcohol dependence. In the first stage of liver disease, fat tissue in the liver accumulates. If drinking continues, the liver then becomes inflamed (alcoholic hepatitis) and fibroids can develop. In the final stages, cirrhosis or scar tissue develops in the liver. This can progress to liver cancer.
Drinking six or more drinks per day for more than 10 years greatly increases your risk of developing cirrhosis. Additionally, about one-third of alcohol-related deaths each year are due to liver disease. 9, 10, 11
Increased Risk of Cancer
Research has shown that excessive drinking can increase your risk of several types of cancer, including:
- Oral and esophageal cancer
- Liver cancer
- Breast cancer
- Colon and rectal cancer
The increased risk of cancer can occur with as little as one drink per day and increases the more you drink. 2,6,9,12
Heavy drinking and chronic exposure to high blood alcohol levels change the way your body functions and cause certain metabolic disorders. These include the build-up of high levels of lipids in the blood and lactic acid in the muscles causing problems with the heart, circulatory system, muscles, and joints.
Other changes in the body from alcohol dependency weaken your immune system and increase blood pressure. 12
Alcohol is a neurotoxin with toxic effects on the brain. Over time, alcohol damages the brain’s cells, tissues, and nerve pathways. This causes cognitive impairment, learning problems, and dementia.
Your mental health is also affected with alcohol misuse being associated with higher rates of anxiety, depression, and suicide. 6,8,12
Hope with Recovery
It’s never too late to stop drinking. The good news is that in many cases, damage caused to your body by heavy drinking may be healed when you quit drinking.1 People with dependency or addiction to alcohol can and do recover and benefit from cognitive behavior programs, rehabilitation, and participating in 12-step programs. If you are worried that you or someone you know might be misusing alcohol, you can contact 800-839-1686Who Answers? to find help.
- Centers for Disease Control and Prevention. (2021, February 16). Alcohol basics.
- Davis, K. (2018, February 28). What effects does alcohol have on health? Medical News Today.
- Hartney, E. (2020, September 20). How blood alcohol concentration (BAC) impairs your body and brain. Very Well Mind. Retrieved from:
- MedlinePlus, (n.d.). Blood alcohol level.
- Centers for Disease Control and Prevention. (2020, December 18). Impaired driving.
- National Institute on Alcohol Abuse and Alcoholism. (n.d.). Alcohol’s effects on health.
- WebMD. (n.d.). What Is alcohol withdrawal?
- American Psychiatric Association. (2013). Substance Use Disorders. In Diagnostic and statistical manual of mental disorders (5th Ed.).
- Centers for Disease Control. (n.d.). Alcohol use and your health.
- Wolf, D.C. (2020, October 15). Cirrhosis. Medscape.
- Merck Manual, Consumer Version. (2019, September). Alcoholic liver disease.
- Zakhari, S. (2006). Overview: how is alcohol metabolized by the body? Alcohol Research & Health, 29(4), 245–254.