What Causes Blackouts and How Do You Avoid Them?

Here's what happens to your brain when you get black-out drunk.

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Ever wake up after a night of drinking with no memory of what happened after that 5th shot of tequila? And, also, whose house is this? Blacking out is a fairly common side effect of hitting the bottle too hard. But what exactly is a blackout and what happens in your brain when drinking that makes you forget?

There are actually two distinct kinds of blackouts, Gizmodo reports. “Fragmentary,” when you forget moments or smaller periods of time, and “en bloc” when you lose hours at a time or an entire night.

For people who experience “fragmentary” blackouts—often known as “brownouts”—memories can usually be restored later on, when the person is reminded of what happened. But for those who experience “en bloc” blackouts, these memories are gone for good.

Both types of blackout are thought to be caused by a neurophysiological, chemical disruption in the brain's hippocampus, a part of the brain where memories are formed. Receptors in the hippocampus transmit glutamate, a compound that carries signals between neurons. Alcohol interferes with these receptors and prevents the neurons from communicating with each other, which ultimately disrupts long-term potentiation (LTP), a process crucial for learning and making memories.

So a person in a blackout is generally able to maintain certain basic functioning, such as language and basic motor skills. But their brain is temporarily incapable of creating new memories.

In general, blackouts are dangerous because they indicate a level of drunkenness that is high enough to lead to unsafe decisions, like unprotected sex or getting behind the wheel of a car. Drinking this heavily over time can put strain on your body and potentially damage your vital organs, including that highly-useful brain. Plus, there’s the pesky problem of not being able to recall what you did or said the night before.

So, how do you avoid them?

Obviously, avoiding alcohol altogether is a surefire way to avoid blackouts. Eating a full meal beforehand also helps. Drinking on an empty stomach can cause blood alcohol levels to rise more quickly. Studies show a dramatic spike in blood alcohol content is the number one cause of a blackout, which usually kicks in at a BAC of around 0.15%, or roughly twice the legal limit for driving.

Women may be more prone to blackouts as their blood alcohol tends to rise faster than men’s. Also, people who have blacked out are more likely to black out again in the future. So it’s recommended to lay off the sauce for a while if this has happened to you.

Does blacking out make you an alcoholic? Not necessarily. Recent studies suggest people who binge-drink socially, like college students, are just as likely to experience blackouts as people who are routine drinkers or alcohol-dependent. Though some research suggests there is a genetic component that makes some drinkers more prone to blackouts, it’s ultimately the quick spike in blood alcohol content that triggers your brain to forget.