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Blood Alcohol Content, What It Means and Its Impact on You

Updated on February 23, 2015
Alcohol is fine in moderation; it's only when we drink a lot that the problems start to be felt.
Alcohol is fine in moderation; it's only when we drink a lot that the problems start to be felt. | Source


Many people enjoy a drink, and whether it's beer in a bar with your friends, a glass of wine with dinner or a cocktail on a sunny day, responsible drinking in moderation is a normal part of people's lives. The amount of alcohol that we have in our body at a specific time can be measured through something called our 'Blood Alcohol Level' and this article explores what that means and the effect that it can have.

Simply put, an individual's blood alcohol level measures the percentage of alcohol (ethanol) in a person's blood. This level is increased by the alcoholic drinks that a person consumes and is reduced by time as a person's body (especially the liver) cleanses the blood and removes the alcohol from a person's system. We'll explore:

  • Factors that affect someone's blood alcohol level
  • How blood alcohol levels are measured
  • The effects of different blood alcohol levels on an individual
  • Reducing blood alcohol level

Factors that affect someone's blood alcohol level

The following factors affect the amount of alcohol in a person's body:

  • The number of alcoholic drinks that they have had.
  • The amount of alcohol consumed in each drink (i.e. the strength and amount of drink consumed).
  • The length of time that the drinks have been consumed over.
  • How long it has been since the person stopped drinking.
  • The person's weight.
  • The speed of a person's metabolism.
  • The person's gender.

Because there are so many factors to take into account, it is difficult to accurately predict exactly how much consuming a specific amount of alcohol will affect a specific individual without directly measuring their blood alcohol level.

Despite this, there are some rough estimates that can be made; for example: A man weighing 160 lbs can expect to increase their blood alcohol level by roughly 0.02 for every drink that they have. In this instance a drink would be considered one shot of liquor or spirits, one glass of wine or one can or bottle of beer.

The strength of the alcohol in what you are drinking directly affects your blood alcohol level
The strength of the alcohol in what you are drinking directly affects your blood alcohol level | Source

How blood alcohol levels are measured

There are a few ways to measure blood alcohol levels, two of the more popular are through 'breathalyzer' tests and through the drawing and testing of an individual's blood.

  • Breathalyzer - A breathalyzer is a small instrument carried by law enforcement officials that can provide a fast and relatively accurate measurement of a person's blood alcohol level. It does this by getting a sample of exhaled breath from a person and performing analysis to find out how concentrated the alcohol is in the exhalation. It is then able to estimate the level of alcohol in a person's blood and if they are legally fit to drive.
  • Drawing and testing blood - Blood can also be drawn from a person and sent to a lab for blood alcohol level testing. This provides a very accurate result on the alcohol in a person's system and is often completed as a follow-up to a breathalyzer test.

Drawing blood is the most accurate way of determining alcohol levels
Drawing blood is the most accurate way of determining alcohol levels | Source

The effects of different blood alcohol levels on an individual

Please note that the blood alcohol levels below and the number of drinks shown next to each are approximate and should not be taken as a guide to how much a specific individual could drink to reach that particular blood alcohol level. Everyone is different and it is important to understand your own tolerance to alcohol and to moderate your drinking accordingly.

Blood alcohol level of 0.0 (equivalent to no drinks)

This alcohol level indicates that there is no alcohol in a person's system and that they are acting, reacting and behaving normally.

Blood alcohol level of 0.01-0.029 (roughly equivalent to one drink)

With this low level of alcohol, an average person will appear normal and specialized testing would probably be required to find out if they had consumed any alcohol as there are unlikely to be any physical or behavioral signs.

Blood alcohol level of 0.03-0.059 (roughly equivalent to two to three drinks)

At this level, the effects of alcohol are more apparent. Individuals with this level of intoxication are likely to experience relaxation, joyful feelings, a reduction in their inhibitions, talkativeness and difficulty with concentration. In many parts of Europe, people cannot legally drive a car with a blood alcohol level of higher than 0.05.

Knowing your limits when it comes to drinking will help to make sure it doesn't get out of control
Knowing your limits when it comes to drinking will help to make sure it doesn't get out of control | Source

Blood alcohol level of 0.06-0.09 (roughly equivalent to three to four drinks)

With concentrations of this level, the effects of alcohol consumption are more pronounced. Individuals will feel more disinhibited and extroverted. They may well have problems with perception, especially depth perception and seeing things in their peripheral vision. They will also encounter problems with reasoning. In the UK and the US, people cannot legally drive a car with a blood alcohol level of higher than 0.08.

Blood alcohol level of 0.1-0.19 (roughly equivalent to four to six drinks)

At this level, individuals are becoming very inebriated. Typical behaviors include boisterousness and mischief-making, a decreased sex-drive, over-expression and possibly anger or sadness. People will start to see significant issues with reflexes, hand-eye coordination and motor control and may experience staggering and slurred speech. It is also possible that people with a low tolerance for alcohol may experience temporary alcohol poisoning.

Blood alcohol level of 0.2-0.29 (roughly equivalent to six to eight drinks)

Individuals with blood alcohol levels above 0.2 are becoming significantly intoxicated. With this much alcohol in their system, people have the possibility of falling into a stupor or falling unconscious, they will have loss of understanding and awareness of their surroundings, impaired sensations and memory blackout.

Regular intoxication isn't healthy
Regular intoxication isn't healthy | Source

Blood alcohol level of 0.3-0.39 (roughly equivalent to eight to ten drinks)

At this blood alcohol level, the amount of alcohol in a person's system is becoming dangerous. They may experience a depression of their central nervous system, likely unconsciousness, problems with their bladder function and their breathing. At this level, there is a risk of death to individuals with poor alcohol tolerance, due to interference with the heart rhythm, breathing and other bodily functions.

Blood alcohol level of 0.4 to 0.5 (roughly equivalent to ten to twelve drinks)

Individuals with this amount of alcohol in their blood should receive medical assistance as there is a significant risk to life with blood alcohol concentrations this high. At this level, there is a general lack of responsiveness and behavior from a person, they may experience a seriously depressed nervous system, there is a significant risk of alcohol poisoning and vital bodily functions may be disrupted.

No. of drinks
Alc. Lvl
Normal behavior
Very little, if any change in behavior
Relaxation, reduced inhibitions, difficulty concentrating
Disinhibition, extroversion difficulty with peripheral vision and depth perception
Poor reflexes and hand-eye coordination; slurred speech; staggering, anger or sadness
Falling into stupor or unconscious; lack of awareness of surroundings; impaired sensations; blackouts
Danger to central nervous system; unconsciousness; impaired bladder function; difficulty breathing
0.4 to 0.5
Seriously depressed nervous system, alcohol poisioning
Severe and immediate risk of alcohol poisoning and death
The impact of the number of drinks on an individual and their blood alcohol level

Blood alcohol level of 0.5 or higher (roughly equivalent to twelve drinks or more)

At this level, an individual is at severe and immediate risk of alcohol poisoning and death. They must receive medical attention as soon as possible.

Reducing blood alcohol level

There are several ways for an individual to manage and reduce their blood alcohol level:

  • Reduce the amount of alcohol that they drink through alternating alcoholic drinks with non-alcoholic drinks.
  • Slowing down their consumption of alcoholic drinks.
  • Consuming alcoholic drinks with a lower 'alcohol by volume' measurement.
  • Drinking over a longer period of time (a person's blood alcohol level drops by 0.01 after every forty minutes or so).
  • Note that caffeine, food, fresh air and the like are not effective ways of reducing blood alcohol levels.

Blood alcohol concentration

How many drinks would you have in an evening?

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In closing

Alcohol can be a perfectly normal part of an individual's life and in moderation can be a good addition to a social gathering. It is important to know your own limits though and controlling your alcohol intake will ensure that you can enjoy your drinks in a safe, secure and responsible way.


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    • Paul Maplesden profile imageAUTHOR

      Paul Maplesden 

      4 years ago from Asheville, NC

      Thanks for making this point, much appreciated.

    • connieow profile image

      Connie S Owens 

      4 years ago from El Cajon, CA

      I would add one more thing to this, if you are a diabetic, untreated, you can test positive for alcohol. But that cannot be an excuse. When I was working in a residential recovery facility, we had clients who tested positive for low levels of alcohol. They always did a gas chromatography in those cases and recommended women were tested for diabetes as soon as possible.

      Voted up and useful. Thank you for this great article.


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