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Alcohol use and memory loss—blackouts?

Dear Alice,

What exactly does "blacking out" from alcohol mean? Can people get so drunk that it is physiologically impossible for them to remember what happened the next day? Also, is it possible for someone to walk around, talk to people, etc., and then have no way of remembering those actions?

Dear Reader,

It’s time to shed some light on alcohol-related blackouts. To answer your question—yes, it’s possible for people to get intoxicated to the point that it is difficult or impossible for them to remember what happened the following day. Blackouts can occur when large amounts of alcohol are consumed quickly, creating a rapid increase in a person’s blood alcohol content (BAC). Blackouts generally begin at a BAC of approximately 0.16 percent or higher, but they can also occur at lower BACs if someone is taking certain medications. The increase in blood alcohol content in the bloodstream affects the functioning of the hippocampus—an area of the brain that plays a significant role in the formation, storage, and understanding of memories. More specifically, alcohol can temporarily impede the ability of information to transfer from short-term memory to long-term storage, which in turn impairs memory creation. There are several risks associated with blacking out and doing so frequently may indicate some degree of alcohol dependence and abuse.

It might be helpful to first understand the different types of blackouts and recognize that the ability to recall memories can vary depending on the type of blackout a person experiences. Blackouts come in two types—en bloc (total) or partial (fragmented). A total blackout often results in a person experiencing complete memory loss (amnesia) of the events that occurred around the time they consumed alcohol. Alternately, with a partial blackout, sometimes called a “grayout” or “brownout”, people often have memory lapses with some recollection. The higher a person’s BAC, the more likely they are to have a total blackout as opposed to a partial blackout. Having a high BAC can also increase your chance of experiencing alcohol poisoning, which when severe enough can lead to death.

The risk of blacking out due to alcohol use varies from person to person based on a variety of factors, but what’s most important to note is that it can happen to anyone who drinks, regardless of their drinking habits. There are, however, certain higher-risk drinking habits that could increase a person's chances of blacking out. Polydrug use—using either illicit or legal drugs in succession—can increase a person's likelihood of blacking out as combining drugs and alcohol can have a harsh impact on memory. The severity of the blackout and the degree to which your memory is affected depends on factors such as your weight, height, how much of each drug you consume, how strong each drug is, and the order of drug consumption. Besides blackouts, other symptoms associated with polydrug use include:

  • Dizziness
  • Lightheadedness
  • Loss of balance
  • Poor judgment and coordination
  • Low blood pressure
  • Slowed breathing
  • Unconsciousness
  • Coma
  • Death

There has also been an increase in the frequency of blackouts experienced by teenagers and young adults who participate in pre-gaming activities—often related to drinking in large groups or before a big event such as a party or sports game. Pre-gaming can be dangerous as it can include playing drinking games that encourage repeated and rapid consumption of alcohol which can quickly increase levels of intoxication. Another risk factor for blackouts is being assigned female at birth. This is due to physiological differences as well as these individuals' innate inhibition to recover more slowly from memory impairments as compared to individuals assigned male at birth.

Contrary to popular belief, it's not always obvious when a person is experiencing a black out, as people often experience cognitive and memory impairments before physical functioning is visibly affected. While usually clearer when people pass out—they stop moving and talking—it can be harder to recognize a blackout as people often appear to be awake and functioning “normally”. This is because they are still able to use their working and short-term memory to carry on conversations and engage in complex behaviors. Yet, the information they gather while experiencing a blackout isn't stored in long-term memory and retrieval of memories can be limited or lost. Sometimes this can lead to potentially serious or even dangerous occurrences that are impossible to remember, which can be troubling or traumatic for the person experiencing it.

Because decision-making and the ability to interpret social signals is impaired while drinking—completely so while blacked out—it may be more difficult for someone to pick up on signs of danger and stay safe. People who are blacked out or experiencing alternate effects of polydrug use may be more easily manipulated or coerced into doing something they would not do while sober. The possibility of experiencing sexual assault increases  when a person is blacked out because they cannot provide affirmative consent. If you choose to drink, consider doing so with friends and other people you trust so you can help to watch out for each other.

So, what can be done to prevent blackouts? One place to start might be by limiting your daily alcohol consumption and drinking in moderation. If you’ve noticed your black outs have been occurring more regularly, consider talking with a health care provider or health promotion professional who can help you determine steps for establishing a lower-risk relationship with alcohol. For those who may be interested in cutting back on or quitting alcohol, the National Institute on Alcohol Abuse and Alcoholism’s Rethinking Drinking offers additional information and resources to help people explore their drinking habits.

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Last updated Mar 03, 2023
Originally published Apr 26, 1996