Because no good drink goes unpunished.
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The price of a night of drinking is very often a hangover. Although hangovers seem like the universe's way of scolding you for that extra espresso martini, or of knocking you down a peg for having too much fun, they're actually caused by the biological process our bodies go through after drinking an excessive amount of alcohol. If you've ever wondered what a hangover truly is, what's making you feel so crummy, or what you can do to ward off the pain next time, here's what health experts and research have to tell us about the science behind the dreaded hangover. 

What exactly is a hangover, anyway?

To put it simply, your hangover is a set of signs and symptoms that result from your body's effort to process alcohol. Hangovers can come in all shapes and sizes and include a myriad of consequences, including fatigue, weakness, thirst, headache, muscle aches, nausea, stomach pain, vertigo, sensitivity to light and sound, anxiety, irritability, sweating, and increased blood pressure. It's not uncommon for your cognitive processes to fall victim to a hangover, too. "Your memory and concentration may also get affected," says Victoria Glass, a physician and medical researcher with the Farr Institute.

This is because alcohol can easily cross the blood-brain barrier, which regulates our central nervous system, says Anthony Puopolo, MD, chief medical officer at RexMD. "This is why alcohol can so easily affect cognition and motor function," he says. "It tends to be tough on neurons and can make it difficult for your brain to, in essence, delineate tasks." This can result in headaches, a common hangover symptom, and lead to morning exhaustion as your brain attempts to catch up.

So what actually causes all of these side effects? According to Dr. Puopolo, it all comes down to your metabolism. It generally takes about one hour for the liver to metabolize one drink (defined in the Dietary Guidelines for Americans as 12 fluid ounces of beer, 5 fluid ounces of wine, or 1.5 fluid ounces of 80-proof distilled spirits).

"When your body (namely your liver) metabolizes alcohol, it produces something called acetaldehyde, a toxic chemical that occurs naturally in things like alcohol and coffee," Dr. Puopolo explains. "In large amounts, it becomes very difficult for your body to break down. Thus, heavy drinking launches your body into overtime to process this excess toxin."

While too much of any alcoholic drink can ultimately lead to a hangover, there's some evidence that certain varieties can trigger a more intense morning-after reaction. During alcohol production, the fermentation process produces extra substances (chemicals and alcohols) known as congeners. (If you've ever heard someone talk about tannins in wine, for example, that's one type of congener). And some types of alcohol contain more congeners than others.

"High-level congener drinks such as tequila, cognac, and whiskey may intensify the hangover," says Dr. Glass. Specifically, this is due to their high methanol content. Methanol, or methyl alcohol, is a congener that occurs in tiny amounts in many alcoholic beverages—and it's actually toxic to humans.

Beyond the cocktail of chemicals your body has to process—and the chemical byproducts produced during the act of processing them—you also feel so terrible after a rowdy night because alcohol is a diuretic and can seriously dehydrate you. Dehydration, of course, can interfere with everything from concentration to digestion, headaches to happiness levels.

What can make a hangover worse?

Some unlucky people are more susceptible to hangovers simply due to genetics. Having a family history of alcoholism may also suggest an inherited predisposition to the way your body processes alcohol, making you more prone to them.

But there are many other immediate factors that can contribute to a nasty hangover. One of them is drinking on an empty stomach, since having no food in your stomach can actually speed up how quickly your body absorbs alcohol. Another is mixing other drugs with alcohol, like nicotine (or cigarettes). Not sleeping well or enough after drinking can increase hangover symptoms—a real catch-22, since drinking disrupts sleep. As Dr. Glass mentions, drinking an excessive amount of darker-colored alcoholic beverages—whiskey, red wine, brandy—is also more likely to make you hurt the following day (but drinking clear, lighter-colored drinks is no guarantee).

Hangover myths you can ignore

There are a lot of hangover myths out there, but most of them are more fiction than fact. 

Are you supposed to eat bread to "soak up" the alcohol?

"As much as it's wise to eat enough before drinking to slow the alcohol absorption, bread is no sponge," says Dr. Glass. 

Is "hair of the dog" a real remedy?

Some people swear by it, but this cure is purely anecdotal. "Hair of the dog is not a real thing," Dr. Glass confirms. Drinking more alcohol to relieve hangover symptoms can actually make you feel even worse, and it just adds more alcohol to your system.

Should you drink more water than usual?

Some people also turn to "pounding water," or drinking as much water as possible to "flush out" the alcohol. While normal, proper hydration is recommended, too much water can be toxic, especially to your kidneys. Dr. Puopolo suggests staying on top of hydration while drinking to avoid intense symptoms in the morning by alternating between cocktails and water.

The hard truth about hangovers

"Ultimately, the best hangover cure is to avoid overdrinking. You won't prevent a hangover because you didn't drink dark liquor, and drinking a beer in the morning won't save you," says Dr. Puopolo. "Drinking in moderation and taking care of yourself is key to avoiding any nasty symptoms the morning after a night out. And the best thing you can do if you are hungover is rest, drink water, and increase your vitamin C and vitamin D levels."