What Actually Happens When You Black Out From Drinking?

Quirky Queries answers your random science questions. If you have a query, let us know!

To be honest, this was a very fun, and also very alarming question to research and write about. A lot of what I learned, especially about the human brain, was surprising, but I was shocked to learn just how potent alcohol is — it can completely shut down entire regions of your brain. 

There are many different types of memories, including long-term, short-term, and muscle memory. These are all stored in different, interconnected regions of your brain. Interestingly, binge drinking does not prevent you from creating or recalling memories. Rather, when you are blackout drunk, what you lose is the ability to store memories. 

As many of us know, alcohol can affect cognitive functions including impulse control, attention, judgment, and decision-making. It does this by slowing down communication between neurons which affects how your brain processes information. Specifically, alcohol binds to receptors for a neurotransmitter called gamma-aminobutyric acid (GABA) which is responsible for calming and sedating your brain. By triggering this receptor, alcohol causes your brain cells to fire less and less frequently. 

According to the National Institute on Alcohol Abuse and Alcoholism (NIAAA), when you drink large quantities of alcohol, it can start to affect a delicate region of your brain called the hippocampus, which is responsible for learning and memory. This typically begins to happen at Blood Alcohol Concentrations (BAC) of about 0.16 percent, which is twice the legal driving limit. An average female begins approaching these levels after about 4 drinks in the span of 2 hours; for an average male, it takes about 5 drinks. 

The percent of “pure” alcohol (expressed here in alcohol  by volume), varies by beverage. From the National Institutes of Health

Buried deep within the temporal lobe, the hippocampus is a very complex part of your brain. Short term memories are transferred here for long term storage. The transfer of memories is a complicated process, and when you drink, communication between neurons in your brain is significantly impaired, making the memory-storing process difficult to impossible. This means that you are still making short term memories while you are blacked out, but you aren’t storing them. These short term memories are shorter than you might think. According to Duke University, they only consist of the last 15-30 seconds. Anything longer than that will be transferred to your long term memory, or, if you are blackout drunk, lost. 

There are different types of blackouts, which relate to the scale of memory loss. A “fragmentary blackout” — also known as a grayout or brownout — is the most common. This is when your memory of events is patchy or foggy. You can remember what generally happened, but there are large dark spots that you can’t recall. This occurs as your hippocampus is beginning to shut down. The second type is known as an “en bloc” blackout and happens when the hippocampus goes entirely offline, and memory formation is completely blocked. If this occurs you won’t be able to remember events at all: it will feel as if they never happened. 

If you look up “blackouts due to drinking,” most of the images you’ll find are of people passed out. This is a common misconception, but “blacking out” is very different from passing out. During the latter, your entire body shuts down, but when you black out, you are still active. You can move around, and because you can still recall the last 15-30 seconds, you can have conversations with people, but brain function is significantly affected, and you lose the ability to store short-term memories. 

So how much do you have to drink before you black out? There is no clear-cut answer.  Your alcohol metabolism depends on your gender, your weight, how quickly you drank, what you ate that day, if you are taking any medications, and many, many other factors. It’s important to remember that even if someone didn’t consume that much alcohol, they could still be very intoxicated and possibly blacked out. 

According to a 2016  study by Reagan R. Wetherill, roughly 50% of drinkers will experience partial or complete memory loss due to drinking at least once in their lifetime. If you decide to drink, it’s important to check in with your friends multiple times throughout the evening to make sure everyone is safe. Although alcohol is one of the most socially accepted drugs, both its immediate and long term effects can be severe. 

If you have a quirky science query, let us know!

This article was edited by Emi Krishnamurthy and Gargi Nigam.