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Blacking Out Vs. Passing Out

definition, suspected causes, and why it is dangerous

Blacking Out


Blackouts are a reaction to the consumption of alcohol which impacts memory.  It’s the inability to recall any memories that may have been formed during the period of intoxication. During this period a person can often remember what they are doing and saying for a two minute period and thus carry on conversations. This makes it more difficult to recognize a person experiencing a blackout. The individual can experience both total memory loss of what happened during the period of intoxication OR partial memory loss where portions of time or specific actions completed while intoxicated cannot be recalled.

Suspected Causes

While the exact cause of individual episodes of blackout can vary, several factors are used as indicators of risk for it. These are:

  • The blood-alcohol level (BAC is very high, typically above a .25).
  • The rate of increase in alcohol in the blood was very fast (guzzling of alcohol, taking shots, especially on an empty stomach).
  • The person is a heavy drinker.
  • The person has a history of previous blackouts (some have predisposition to blackout even with lower BAC).

Why is it Dangerous?

  • Social drinkers can blackout too and females more likely to experience blackouts than males.
  • Due to the high level of intoxication needed to experience a blackout, other psychological processes may also be impaired.
  • Impairments in judgment, decision-making, and impulse control could lead an individual to make potentially hazardous choices during blackouts.
  • The total number of blackouts experienced by students appears to correlate with lower grade point averages and other indicators of problem drinking, the researchers said. Additionally, they learned that while female students tend to drink less heavily than their male counterparts, they were just as likely as males to experience blackouts - and that, they say, could put females at greater risk for a variety of consequences.



White, A.M (2004). What Happened? Alcohol, Memory, Blackouts and the Brain.  National Institute on Alcohol Abuse and Alcoholism. Grant AA-12478.

White, A. M., Jamieson-Drake, D.W., & Swartzwelder, H.S. (2002). Prevalence and correlates of alcohol-induced blackouts among college students: Results of an E-mail survey. Journal of American College Health, 51(3), 117-119, 122-131.

Passing Out


Passing out from alcohol is when an individual loses consciousness due to a dangerously high blood alcohol concentration.  Someone passed out could appear to have fallen asleep, but cannot be woken up.  Alcohol use leading to passing out could also lead to breathing less than 8 times per minute, uncontrollable vomiting, bluish or pale skin, confusion, seizures, or uneven breathing.Passing out is not uncommon across the life span, but passing out from alcohol use is very dangerous.

Suspected Causes

Alcohol lowers blood pressure. If someone is sober, their body constricts their veins upon standing up so as to increase blood pressure and prevent the person from passing out as their blood falls due to gravity. Even with low-risk drinking (2-3 drinks per occasion), alcohol prevents the blood vessels from constricting, and blood pressure drops twice as much when the person stands up as it would if they were sober.

  • Alcohol is a diuretic, and causes your body to dehydrate.
  • Alcohol also lowers your body temperature, and can cause you to become hypothermic.
  • Alcohol can also cause hypoglycemia, which can cause a coma.

Why is it Dangerous?

  • Drinking enough alcohol to reach the point of passing out can happen very quickly, especially when drinking shots. This means that a person can drink enough to cause them to pass out, but not pass out for a while longer (and therefore, possibly continue to drink) due to the time the body needs to process alcohol.
  • Drinking to the point of passing out happens much faster when the person has not eaten. On an empty stomach, 20% of alcohol is absorbed directly from the stomach and reaches the brain in less than 60 seconds.
  • A person can move from sleeping to unconsciousness without others noticing. This is the danger in allowing someone with alcohol poisoning to “sleep it off.”
  • Alcohol also inhibits the gag reflex, which can cause a person who is unconscious to aspirate their own vomit, causing death.