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NIDA. (2016, April 4). The Science of Drug Testing: How Alcohol Breath Tests Work. Retrieved from

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The NIDA Blog Team
April 4 2016

April is Alcohol Awareness Month—a good opportunity to take a moment and learn about alcohol’s effects on health, and the potential problems associated with drinking too much. On this blog we’ve discussed alcohol from many different angles; now let’s take a look at alcohol breath tests.

These tests are used by police to indirectly measure how much alcohol is in a person’s blood. (Alcohol breath tests are usually given at traffic stops—much easier and safer than trying to do blood tests at the side of the road!) How do the tests work? Check out this infographic, and read more below:

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  • The Breathalyzer, the most famous portable device to test breath alcohol content, was invented in 1954.
  • Alcohol breath-testing devices use the amount of alcohol in exhaled breath to calculate the amount of alcohol in a person’s blood, also known as blood alcohol concentration (BAC). Here’s how:
    • When a person drinks alcohol, it goes into the stomach and small intestine and is quickly absorbed in the blood.
    • Within minutes of a person having an alcoholic drink, that person’s BAC can be measured. BAC usually reaches its highest level about an hour after drinking.
    • About 90 percent of any alcohol consumed is broken down by the liver; the rest is eliminated through urine and breath.
    • The breath-testing device converts the amount of alcohol in the breath to a corresponding BAC.
  • Anywhere in the United States, an adult driver’s BAC cannot legally be over 0.08 percent. All states also have “zero tolerance” laws for drivers under the age of 21; driving with any detectable amount of alcohol is illegal for those who are underage.
  • The BAC limit was set at 0.08 percent for adults because the National Highway Traffic Safety Administration sponsored several studies on impaired driving, and found that virtually all driving-related skills are substantially impaired at that level.
  • How quickly a person’s breath alcohol content becomes elevated and how long it stays that way depend on many factors, including the person’s weight, sex, how much alcohol they’ve had, and when they last ate.
  • This specific kind of test only works with alcohol. Scientists are working on a similar way to measure impairment from marijuana.