Omar Bustamante/FUSION

You had a few too many Manhattans. You're less coordinated. Your reflexes aren't as sharp as usual. Your speech is slightly slurred, but making conversation seems easier. Suddenly the dude sitting across the bar looks more like Ryan Gosling than Steve Buscemi. So, of course you catwalk (translate: stumble) toward him and lay one on him. Inhibitions be damned.

That's the beauty‚ÄĒand danger‚ÄĒof alcohol. It's easy to blame your "out of character" shenanigans on the a-a-a-alcohol. After all it was the¬†Goose that got you feeling loose. This is part of the reason it's¬†so popular. In 2013, roughly 60% of people 18 and older said they'd had a drink in the past month. I have friends who drink a couple of nights a week and I'm sure you do too.

Alcohol is the most commonly used addictive drug in the U.S. It's a social drug available almost everywhere. In 2014, people drank a combined 249 billion liters, or 66 billion gallons, according to The Economist. (Most of that was beer.)

It's one of the oldest recreational drugs in existence, but is still hip, hosting "happy hours" and playing a recurring central character in movies like The Hangover, The World's End, Beerfest, Sideways and many, many others.

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So how does it make our brains feel so good… and then feel so bad? As you're drinking your favorite spirits, you start to feel giddy, relaxed and more excitable, which makes your social interactions less awkward and more enjoyable. The active ingredient in your microbrew or margarita is ethanol. Ethanol subdues brain cells in the cerebral cortex, the part of the brain responsible for high-level reasoning. So the cells responsible for saying, 'That's not a good idea,' get tuned out. It does the same thing to the cerebellum, the part of your brain that's involved in coordinating movement and balance, resulting in that tell-tale drunken strut.

How does this all happen? Like other drugs (flakka, molly, caffeine and adderall), ethanol disrupts the amount of chemical messengers in the brain. Specifically it screws around with glutamate and gamma-aminobutyric acid, or GABA for short. When you drink, alcohol goes from your bloodstream to the brain. There, it amplifies the effects of GABA, a brain chemical that prevents some neurons from sending messages to each other. Think of it as a kind of silencer, keeping neuron "noise" down so that your brain can focus on the most important signals. If your brain were a theater, GABA would be the "shusher" responsible for quieting down those not on stage.

GABA does its shushing by controlling the flow of negatively charged particles, called ions, through the tiny channels on brain cells. Too many negative ions in a brain cell shut it down. So when GABA wants to shush a brain cell, it lets the ions flood in. When alcohol comes along, it floods the brain with GABA, which results in an increased flow of brain-cell-shushing ions. (This is why you can't drink if you're taking drugs like Xanax or Valium, which crank up the amount of GABA in your brain. It'd be too much sedation for your body to handle.)

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Alcohol also blocks glutamate, a molecule that typically activates neurons, so you get a doubly inhibitory hit. (Glutamate is a gatekeeper, like GABA, but it lets in positive ions that get brain cells to send messages to each other.) So when you drink alcohol, you're essentially turning off two systems of your brain.

That's why alcohol is typically regarded as a depressant. Turning the volume down on the reasoning part of your brain, and the balancing part of your brain, add up to you feeling more relaxed and less coordinated the more boozed up you are. After a couple of shots of tequila, you may suddenly find yourself doing things your sober self wouldn't, like going up to a romantic prospect, dancing on a tabletop, or telling some embarrassing stories from your youth. Basically, you're not thinking straight, though you may think otherwise.

It takes a while for all this to right itself. People who drink too much develop a dependency because this imbalance gets even more out of whack. Their GABA stores are depleted, and neurons in their brain become hypersensitive to glutamate. That makes people feel jittery and anxious, and accounts for some of the feelings of withdrawal people experience when they stop drinking.

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It's important to remember that alcohol, like most drugs, affects different people differently, though people typically feel its effects after one or two drinks. (One drink is equal to 0.6 ounces of pure ethanol, 12 ounces of beer, 5 ounces of wine; or a 1.5 ounces shot of 80-proof hard liquor.) How much you're able to drink before your high plummets into feeling ill or blacking out depends on how much hooch you usually consume, plus your age, gender, size and your genetic background.

People tend to black out when they've had too much to drink too quickly, leading to higher levels of alcohol in the brain. It's unclear why some people black out and others don't, but some research suggests that the front part of your brain, which is involved in storing memories, is less active.

You experience hangovers the next day, in part due to dehydration. Whether you feel hungover the next day depends on your weight and gender. The average dude will experience some hangover symptoms after five to eight drinks, while ladies can only drink three to five, according to John Hopkins.  Alcohol also signals your immune system to release molecules that prevent inflammation, and these can result in an "inability to concentrate, memory problems, decreased appetite and loss of interest in usual activities," according to the Mayo Clinic. Booze also causes your blood vessels to expand temporarily, which may result in a throbbing headache, according to the Mayo Clinic.

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There is some research that shows that, in moderation, certain types of alcohol can actually have beneficial health effects. For instance, it may help some people fall asleep and or experience more deep sleep, but only during the first half of the night. But, the alcohol-induced chemical imbalances screw you, and your sleep ends up betting disrupted.

At the extreme, people can develop all sorts of brain damage. Brain cells can start to shrivel, leading to altered motor coordination, temperature regulation, sleep, and mood, as well as loss of memory. For instance, patients can develop conditions like alcohol-related cerebrovascular disease, which is caused by changes in the brain's blood vessels, and dementia, also known as Korsakoff syndrome. Patients with these disorders suffer from memory problems.

When blood flow to the brain changes, brain cells are starved of nutrients and oxygen, leading to cell death, so patients with cerbrovascular disease have a lot of the same symptoms as Alzheimer's. It's common in older adults, but the risk of developing it is much greater in heavy drinkers. Drinking heavily can trigger your body to start releasing stress hormones that constrict blood vessels, which elevates blood pressure. Over time, high blood pressure makes blood vessels less elastic, which puts more stress on your heart. This all leads to altered blood flow throughout your entire body.

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People with Korsakoff often have issues learning new information; they also have problems with short-term memory. For instance, they might be able to carry on a conversation, but not remember whom they spoke to or what the conversation was about just moments later. The condition is caused by a lack of thiamine, or vitamin b-1. Thiamine is important in helping cells in the brain harness sugar to produce energy and in the cellular machinery that produces the chemicals brain cells use to communicate with each other. Your body can't make thiamine. You get it from the food you eat. Scientists think that people with alcohol dependencies may not be getting enough in their diets, or that the way the body metabolizes the thiamine they do ingest gets screwed up.

As you may know, alcohol also damages the liver, which breaks down alcohol and alcohol-associated toxins. When liver cells don't function properly, it can't break these bad molecules down. They eventually end up in the brain, where they cause further damage.

Sorry to put a damper on happy hour!

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For more on drugs, check out Drug Wars.

Daniela Hernandez is a senior writer at Fusion. She likes science, robots, pugs, and coffee.