How Alcohol Works

Blood Alcohol Concentration

drunk guy in bear suit drunk guy in bear suit
Someone who's blood alcohol content is between 0.03 to 0.12 percent probably has impaired judgement and they may be more impulsive than if they were sober. PeopleImages/Getty Images

If you have seen someone who has had too much to drink, you've probably noticed definite changes in that person's performance and behavior. The body responds to alcohol in stages, which correspond to an increase in blood alcohol concentration.

Blood alcohol concentration (BAC) refers to the percent of alcohol in a person's blood stream. A BAC of .10 percent means that an person's blood supply contains one part alcohol for every 1,000 parts blood. As we already mentioned, several affect BAC, including body weight, biological sex, how many drinks the person has consumed (and how fast), medications and more. But the body responds to the level of alcohol in the blood, too:

Euphoria (BAC = 0.03 to 0.12 percent)

  • They may become more self-confident or daring.
  • Their attention span may shorten.
  • They may look flushed.
  • Their judgement may not be as sharp and they may be more impulsive; they might say the first thought that comes to mind, rather than an appropriate comment for the given situation.
  • They may have trouble with fine movements, such as writing or signing their name.

Excitement (BAC = 0.09 to 0.25 percent)

  • They could become sleepy.
  • They might have trouble understanding or remembering things (even recent events).
  • They might not react to situations as quickly.
  • Their body movements may become uncoordinated.
  • They may begin to lose their balance easily.
  • Their vision could become blurry.
  • They may have trouble sensing things (hearing, tasting, feeling, etc.).

Confusion (BAC = 0.18 to 0.30 percent)

  • They are likely to be confused — they may not know where they are or what they are doing.
  • They may be dizzy and stagger on their feet.
  • They might be highly emotional, aggressive, withdrawn, or overly affectionate.
  • They may not see clearly.
  • They may be sleepy.
  • They likely have slurred speech.
  • They may have uncoordinated movements (trouble catching an object thrown to them).
  • They may not feel pain as readily as a sober person.

Stupor (BAC = 0.25 to 0.4 percent)

  • They may barely be able to move at all.
  • They may not be able to respond to stimuli.
  • They may be unable to stand or walk.
  • They may vomit.
  • They may lapse in and out of consciousness.

Coma (BAC = 0.35 to 0.50 percent)

  • They are unconscious.
  • Their reflexes are depressed (i.e. their pupils do not respond appropriately to changes in light).
  • Their skin feels cool to the touch (lower-than-normal body temperature).
  • Their breathing slows and becomes more shallow.
  • Their heart rate may slow.
  • Their life could be in danger.

Death (BAC more than 0.50 percent)

  • The person usually stops breathing and dies.