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10 Facts About Blacking Out That Actually Make So Much Sense

An explanation for all those nights you can't remember.

Ever go out drinking one night and wake up the next morning with absolutely no recollection of what happened?

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Everyone knows drinking too much can lead to a blackout. But nobody really understands why.

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What about alcohol makes us forget things? And why does it only happen to certain people, on certain nights, or with certain drinks?

To get to the bottom of this, we spoke with Aaron White, PhD, senior scientific advisor to the director of the National Institute on Alcohol Abuse and Alcoholism (NIAAA), and Dr. Matt Sztajnkrycer, emergency medicine physician at Mayo Clinic in Rochester, Minnesota, about what really happens in your brain when you drink and how that can lead to blackouts (and everything that goes with it).

Alright, here we go.

When you drink, alcohol affects almost every single part of your brain.

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White says it only takes a couple of drinks — depending on genetics and tolerance — for alcohol to enter your bloodstream and make its way to your brain, directly interfering with the areas that tell your body what to do. Here are the areas primarily impacted by booze:

* Reward pathway: Controls feelings of euphoria, making you feel good.

* Cerebellum: Controls motor coordination: balance, movement, reaction time.

* Frontal lobe: Controls behavior, decision making, and impulse control.

* Amygdala: Makes you feel anxious or afraid when you’re in danger.

Most parts of your brain can develop a certain amount of tolerance to alcohol, which is why sometimes you can function completely fine even when you're blacked out.

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White says that while you’re drinking your brain can develop what’s called an acute tolerance — a resistance to the effects of drugs or other things with just a single exposure to the drug — which means your brain is effectively learning how to minimize the effects of the alcohol.

Most parts of your brain can also develop a long-term tolerance to alcohol, which means the more experience your brain has with it, the more tolerance it'll be able to build up, and the more you'll be able to function normally even with a high blood alcohol content (BAC). White says this is why some people can be absolutely hammered, but walk around and talk like they're completely fine; their cerebellum, which controls their motor coordination, has developed a higher tolerance.

But the hippocampus can't build up long-term tolerance. And blacking out happens when your hippocampus is literally incapable of creating memories.

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White says when you're at a BAC of 0.08 to 0.1, the alcohol starts to affect the hippocampus, which is the area of the brain that’s in charge of consolidating information from your sensory organs, your body, your thoughts, and your feelings to create memories.

As your BAC climbs, there are two main reasons your memory gets cloudy: the hippocampus isn’t getting as much rich information from the brain about what's happening, and the alcohol is blocking certain receptors, so that even information that gets into the hippocampus is unlikely to be stored as a memory.

So if you're a heavy drinker, you may develop a tolerance that helps you speak and keep balance, but not for your memory. White says that’s probably why alcoholics are so likely to report blackouts. Because they can get to very high BAC levels and function, but aren’t able to make new memories.

There are two types of blackouts: fragmentary blackouts and en bloc blackouts.

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A fragmentary blackout — what most people call a brownout — is when you have some fuzzy memories from when you were drinking and then periods of missing time, White says. For example, if you remember walking into the bar, and then remember being at Denny’s, but then the next memory you have is brushing your teeth, then you had a fragmentary blackout.

An en bloc blackout — which is much more severe and less common — is when an entire chunk of your life is gone and no matter how hard you try, you can't bring back any memory of what happened. So if you started drinking at a friend's house and then woke up the next day in your bed, with no recollection of how you got there, then you had an en bloc blackout.

The type of blackout you have is going to be determined by the amount of alcohol you drink and the amount of time you drink it in. The more alcohol you drink the more the receptors are going to be blocked and the hippocampus won't be able to make memories.

The odds of blacking out are much much higher when you reach a high BAC quickly.

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White says that it's not necessarily the amount of alcohol you drink, but how fast you drink it, that matters. So if you're ripping shots or bonging beers, you can black out much easier than if you were pacing yourself.

What many people don't realize is that if you drink slowly over three hours, you can reach the same BAC you would throwing back a few shots in an hour, only you won't black out. This is because when you drink slowly, your brain has more time to adjust to the alcohol, which allows it to develop an acute tolerance, and fight off its effects.

The NDMA receptor in the hippocampus — critical for processes such as learning and memory — can also build acute tolerance, just not long-term tolerance. So, that's why you'll be able to keep from blacking out if you space out your drinks.

Some people are just predisposed to blacking out more frequently.

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Unfortunately, Sztajnkrycer says there are people who are much more likely to black out than others. It also seems to be more common in women; while researchers aren't exactly sure why, studies have found it most likely has to do with other factors, like body size, what you're drinking, and drinking on an empty stomach.

And research shows you'll probably black out more easily if you're drinking wine or liquor as opposed to beer.

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Sztajnkrycer says this is because drinks like liquor and wine usually have a higher alcohol concentration than beer. For instance, Budweiser is 4.2% alcohol by volume (ABV), Yellow Tail Merlot is 14% ABV, and Jack Daniel's Whiskey is 40% ABV.

Plus, you typically drink these more quickly. It's a lot easier to throw back four shots then it is to chug four beers.

So when do the lights go back on? That's usually a matter of time and sleep.

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En bloc and fragmentary blackouts end when your body has finally metabolized the alcohol, Sztajnkrycer says. "It's going to depend on how much alcohol you’ve drank, if you're still drinking alcohol on top of that, your genetic predisposition, and the amount of time in which you consumed all the alcohol."

He says most people find they "black back in," or are able to start making memories again, once they've gone to sleep and woken back up. That's because being asleep gives people the time they need for their body to metabolize the alcohol.

Certain medications and drugs can make it more likely — and more lethal — to black out.

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White says that any medication with a sedative affect — benzodiazepines (Xanax), Ambien, or opioids like oxycodone — can make it easier for you to black out, and possibly even die.

This is because alcohol shuts off brain areas by activating a neurotransmitter called GABA, which is what White calls "the brakes" in the brain — what helps everything relax and slow down. When the GABA receptor is activated, a neuron is less likely to generate signals, so it's the equivalent of taking a volume knob and turning it down. Less signals means less thinking, less memories, and basically less being alive.

Blacking out can be extremely dangerous. Like, a lot more dangerous than people think.

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"Research has shown that the level at which you're blacking out can be much too close to the level that could possibly kill you," White says. "The medula and the pons, in your brainstem, control all of your vital reflexes. If you switch them off, you can die."

For example, in some cases when a person is en bloc blacked out and pukes themselves, they've drank so much alcohol that their reflexes have been shut off and the person can’t breathe and can't wake up, therefore they suffocate on their own vomit.

Bottom line: Blacking out is not a good place to be, so please pace yourself when drinking.

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White says the best way to prevent blackouts is to drink at a reasonable pace or stick to drinks with a lower alcohol concentration. Eating a meal beforehand and drinking water between alcoholic drinks will help, too.

Also, don't take shots.

Stay responsible, and happy drinking! 🍻

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