What Really Happens When You Black Out 

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Most of us have been there. You wake up, blood-shot eyes, messy hair and the biggest headache of your life – but you can’t remember anything from the night before. How many drinks did you have last night? Why are there 23 missed calls on your phone from your best friend – or worse, your mother? How exactly did you get home? Am I in my house? So. Many. Questions.

It seems like a typical case of blacking out from a night of partying.

But do you know exactly what happens to your brain when you black out? This article attempts to explain what really goes on in your brain when it happens, the risks involved and how to avoid it.

  • What is a blackout? Fragmentary vs. en bloc blackouts

Blackouts in general are defined as alcohol induced amnesias in which a person may no longer be able to remember some or all of the events that transpired during an episode of blacking out. A blackout is vastly different from “passing out” from drunkenness in which a person loses total control or loses consciousness due to excessive amounts of alcohol in the system. Most people who blackout don’t realize they can no longer remember anything and they figure it out only when it’s too late – when they sober up.

There are two types of blackouts, one is referred to as fragmentary the other is referred to as an en bloc blackout.

Fragmentary blackouts. Fragmentary blackouts are often referred to as “brownouts” and are nearly as severe as en bloc blackouts. People who have undergone fragmentary blackouts can usually recall events throughout the day or once a trigger jogs their memory.

En bloc blackouts. En bloc blackouts are when the person really does not remember anything that has happened. The person could have seemed conscious and cognizant during the event but it will seem like it never happened to them because they will have no memory of it whatsoever.

  • How does it happen?

There are a couple of theories about how a blackout happens. One is that alcohol floods your hippocampus (not literally) and prevents new information from coming in, or the hippocampus may have difficulty connecting the new information together.


Alcohol, it seems, impairs the encoding of contextual memories within the hippocampus.

The hippocampus is the area of the brain responsible for turning short-term memories into long-term ones, which is why a person who has blacked out can respond normally to social situations and even take themselves home but will have difficulty remembering what happened the night before or how exactly they got to their houses.

Another theory is that alcohol binds with GABA receptors in the brain. Alcohol, unlike other molecules, readily crosses the blood brain barrier. Once in your brain’s blood supply, alcohol can readily react with chemical receptors in your brain cells. One such receptor is the GABA receptor. GABA (gamma-aminobutyric acid) closely resembles ethanol molecules. For this reason, ethanol can mimic GABA and disrupt its activity. By flooding the brain, as in the case of excessive alcohol consumption, alcohol binds with all GABA receptors, effectively blocking neurological signals.

So a lot of times it’s not that the signal has not been received by the brain, it’s that the neurons can no longer send the signal.

  • What are the risks?

There are numerous risks associated with blacking out and excessive alcoholic consumption.

Among the chief risks would be brain damage and unconsciously putting yourself in harm’s way. Many people, be it male or female, have woken up in a stranger’s home or vehicle without any idea how they got there. It is not uncommon for people who experience blackouts to be sexually harassed, violated or have something stolen from them. The worst part about blacking out is that while you are conscious, you can behave normally, leading your companions to think that you are alright and of sound mind. No alarms go off in their minds and you could be left vulnerable in risky situations.

Women in particular, because they have less alcohol dehydrogenase than men, are more prone to experience blackouts. Alcohol dehydrogenase is the enzyme that breaks down alcohol into less toxic metabolites.

  • How to avoid a blackout?

The best way to avoid a blackout, if abstaining from alcohol is not possible, is to stick to beer, wine or cocktails or any other drink that contains a lot of water. Steer clear of shots because it is quite easy to have too much of them in a short amount of time. Another trick is to drink slowly, pace yourself and sip your drink instead of gulping it. Consuming your alcohol slowly will allow your body to break down the alcohol before it can cause you to black out.