Blood alcohol concentration (BAC) is the amount of alcohol in a person’s bloodstream. A BAC above 0.40% is considered dangerous. In some cases, it may prove fatal if a person does not receive emergency care.

Higher percentages of alcohol in the blood may be fatal for some people. What is considered life threatening varies on the body’s tolerance level, reaction to alcohol, and amount of alcohol consumed, among other factors.

This article looks at fatal blood alcohol levels, signs and treatment of alcohol overdose, what BAC is and signs of different BAC levels, and support with managing or quitting drinking.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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A BAC above 0.40% has a risk of serious complications, including coma and death, according to MedlinePlus, a service of the National Library of Medicine.

The amount of alcohol it takes to prove fatal for a person may vary by individual factors, such as body weight and metabolism.

As BAC increases, so do alcohol’s effects on a person’s body and motor functions.

BAC may also keep rising even when a person has stopped drinking or is unconscious: Alcohol continues to enter the bloodstream and circulates throughout the body.

This is when BAC may increase to dangerous levels if the person does not receive emergency care.

Binge drinking and overdose

Binge drinking refers to a pattern of drinking that brings BAC to 0.08% or higher in a short period. This typically occurs after females consume four drinks or more and males consume five drinks or more during a 2-hour period.

Anyone who consumes too much alcohol too quickly may be in danger of an alcohol overdose, also called alcohol poisoning.

An alcohol overdose occurs when a person has so much alcohol in their bloodstream that certain bodily functions may begin to shut down.

Signs of an alcohol overdose include:

Blood alcohol concentration (BAC) is the level of alcohol present in a person’s blood after consuming alcohol.

The level depends on the person’s:

  • body weight
  • age
  • sex
  • metabolism
  • physical and mental state
  • food intake

It also depends on:

  • amount of alcohol consumed
  • the type of alcohol and its strength
  • how long the drinking episode was

The body can only metabolize about one drink per hour. If someone consumes more than one drink per hour or drinks quickly, the alcohol stays in the body until it metabolizes it.

Calculating BAC

A person can calculate their BAC with online calculators, which estimate a person’s BAC based on:

  • sex assigned at birth
  • body weight
  • type of alcohol
  • quantity
  • time since the first drink

The first two to three drinks typically lead to a BAC of 0.01–0.07%.

As an example, for a female who weighs 150 pounds (68 kilograms), their BAC will be .06% after two beers. For a male who weighs 200 pounds (90.7 kilograms), their BAC will be 0.04% after two beers.

However, the above is not entirely accurate because of other important factors that a calculator cannot account for, such as:

  • individual metabolism
  • strength of drink
  • food intake before and during drinking

What are the signs of different BAC levels?

According to the National Institute on Alcohol Abuse and Alcoholism, different BAC levels can cause varying levels of impairment:

  • 0.00–0.05%: This BAC elicits sleepiness and relaxation. It may also cause mild impairment in:
    • speech
    • balance
    • attention
  • 0.06–0.15%: A person may perceive more beneficial effects from drinking. It may also impair the following functions to a moderate degree:
    • balance
    • motor function
    • attention
    • memory
    • impaired speech
    • impaired driving skills
    • aggression
    • risk of injury
  • 0.16–0.30%: This BAC causes severe impairment in most motor functions, reaction times, and a person’s judgment skills. Some people may also experience:
  • 0.31–0.45%: This BAC range is life threatening and puts a person at risk of alcohol overdose. A person’s vital life functions experience suppression, which may have fatal consequences.

If someone is experiencing any of the above symptoms during or after drinking alcohol, a person should call 911 or get them emergency medical care.

An alcohol overdose requires hospitalization so doctors can monitor a person’s condition for any complications. The person usually receives intravenous (IV) liquids. In some cases, doctors may also give them life support.

Treatment may also involve:

  • general observation and monitoring
  • glucose administration via IV
  • medications for any associated symptoms
  • frequent assessment of breathing

When the effects and the alcohol itself have worn off, medical professionals may assess a person’s risk of having an alcohol use disorder (AUD), recommend next steps, and suggest referrals or relevant treatments.

People who misuse alcohol may have AUD. Some people with AUD have developed a dependence on alcohol to function. They may experience alcohol withdrawal symptoms if they abruptly abstain from drinking. In these cases, a person needs to consult a doctor to determine how to best treat their AUD.

Treatment or support to help reduce or stop drinking may include:

  • medications
  • 12-step programs, such as Alcoholics Anonymous (AA)
  • entering an inpatient rehabilitation unit
  • outpatient treatment
  • mental health care, such as individual therapy and group therapy

Safe drinking tips

If a person does not want to stop drinking or is not yet ready to quit, there are still ways they can stay safe while drinking.

For instance, a person can:

  • limit alcohol consumption to recommended levels, which are:
    • 2 drinks or fewer per day for males
    • 1 drink or fewer per day for females
  • not drink alcohol when taking medications or receiving treatments that may react with alcohol
  • be sure to eat and drink more water while drinking alcohol
  • keep track of how many drinks are consumed
  • avoid mixing types of alcohol
  • avoid drinking games

A BAC level above 0.40% increases the risk of serious complications, including coma and death.

A high BAC level impairs balance, speech, and motor function. Severely high levels may result in an alcohol overdose and be life threatening.

Signs of an overdose include confusion, unconsciousness, vomiting, and more. A person should seek emergency medical care to treat an alcohol overdose.

People typically require hospital treatment for an alcohol overdose so doctors can monitor their condition and administer any medications or fluids via IV.

Medical professionals may recommend additional treatment, such as medications and therapy, for someone who has experienced an alcohol overdose.

People who want to practice safe drinking can limit their consumption, avoid mixing alcohol with medications or other types of alcohol, and speak with loved ones or a doctor for longer-term support.