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The Science Behind Blacking Out


Have you ever woken up panicked and confused, wondering how you got home after a night out drinking with friends? If this has happened, you might have experienced an episode of alcohol induced amnesia, also known as a blackout. This is different than passing out or losing consciousness. Your friends may report drinking and talking with you during the evening and you may have even driven home – but your memory of some or most of the night is wiped away.

Although blacking out is not uncommon – particularly among young people who drink heavily – it is poorly understood. Alcohol-induced impairment is dangerous and can be unpredictable.

What is a Blackout?
Researchers have identified two types of blackouts:

  • En bloc, or complete blackout: when a person who had been drinking has an inability to recall entire events during the drinking period of time
  • Fragmentary-memory loss: when a person who had been drinking can only recall some portion of the events during the drinking period of time
    En bloc blackouts happen when information is not successfully transferred from short-term to long-term storage during a drinking episode. The person who is drinking can sufficiently keep information in short-term memory to engage in conversations, drive a car, and participate in other complicated activities. However, all this information is completely lost as the brain fails to transfer the person’s short-term memory information to long-term memory storage. Indeed, “the defining characteristic of a complete blackout is that memory loss is permanent and cannot be recalled under any circumstances,” according to a summary study looking at alcohol-induced blackouts.
    Fragmentary blackouts are more common and occur when memory formation – the transfer from short- to long-term storage – is partially blocked. Unlike en bloc blackouts, fragmentary blackouts allow for recall of all memories that were stored during the drinking event, but successful recall may involve a bit of effort and prompting.

What Causes a Blackout?
Early studies on blackouts demonstrated that although alcohol is necessary for initiating a blackout, a large quantity of alcohol alone is not sufficient to cause a blackout. In fact, people sometimes have a blackout even when not drinking at their highest level. Factors such as how alcohol is ingested, gender, and genetic susceptibility all play a role in determining a person’s propensity for blackouts. Although having a single blackout by itself may not be sign of alcoholism, repeated blackouts are very often associated with having an alcohol use disorder and being at risk for chronic alcoholism.

According to researchers, gulping drinks and drinking on an empty stomach could also increase a person’s risk of a blackout, as these behaviors raise an individual’s blood alcohol concentration. Additionally, there are gender differences in alcohol-induced blackouts. Women are at greater risk than men of experiencing a blackout even with lower levels of alcohol consumption. This risk is higher in women because:

  • Women have considerably less water in their system as compared to men, so alcohol is less diluted in the bloodstream.
  • Women have a significantly lower concentration of alcohol dehydrogenase (ADH) – the enzyme that metabolizes alcohol before it passes into the bloodstream. Therefore, women have a higher blood alcohol content and experience greater intoxication than men per amount of consumed alcohol.
  • Women generally have more body fat than men. Given that fat does not directly absorb alcohol, they maintain higher concentrations of alcohol in their bloodstream relative to men.

The Dangers of Blacking Out
Blackouts can be dangerous for a number of reasons besides damage to your memory. According to the National Institute on Alcohol Abuse and Alcoholism, a study of college students who blacked out found that the students “reported learning later that they had participated in a wide range of potentially dangerous events they could not remember, including vandalism, unprotected sex, and driving.” The risk for young women who have alcohol blackout may be no different from those who have been given Rohypnol, the date-rape drug. They may experience forced, unwanted, or regretted sexual experiences.

Binge drinking culture in colleges and universities creates increased risk for blackouts and their many negative consequences. Students should be informed of the risks associated with alcohol use, including blackouts, and those who are of legal drinking age should be given guidelines to consume alcohol responsibly if they do decide to drink.

Source: The National Center on Addiction and Substance Abuse (CASA)

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