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Unfortunately, we don’t know how to cure hangovers yet. However, we DO know a lot more about how to make sure you wake up with a hangover. Avoiding some of these behaviors could help you feel better the morning after.

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The Alcohol Hangover (2000)
Acetate Causes Hangovers (2010)
Food-induced lowering of blood-ethanol profiles and increased rate of elimination immediately after a meal (1994)
Role of Tobacco Smoking in Hangover Symptoms Among University Students (2013)
Urine methanol concentration and alcohol hangover severity (2017)
Alcohol Hangover: Underlying Biochemical, Inflammatory and Neurochemical Mechanisms (2019)
The Role of Beverage Congeners in Hangover and Other Residual Effects of Alcohol Intoxication: A Review (2010)
Intoxication with Bourbon versus Vodka: Effects on Hangover, Sleep and Next-Day Neurocognitive Performance in Young Adults (2010)

For as long as humans have drunk alcohol, we've also been looking for relief from hangovers.  Unfortunately, we don't know how to cure them yet, or at least nothing definitive, but we know a lot more about how to make sure you do wake up with a hangover, so avoiding some of these behaviors will hopefully ease that morning after headache.

This one might seem obvious, but you can't get an alcohol-induced hangover without alcohol or more technically, ethanol, and while that seems silly to say, booze is the only consistent theme in our definition of hangover.  That's because everyone's hangover symptoms are different, ranging from a little bit of queasiness to brain melting headaches, so when researchers study hangovers, they'll usually characterize it as a number of symptoms that follow alcohol consumption and metabolism: headaches, fatigue, nausea, and so on.  Then, those symptoms have to get bad enough to disrupt your daily life, but our methods for measuring hangovers or predicting their occurrence can be hit or miss. 

By the time you wake up with your head full of regret, your body has already metabolized, or processed, the ethanol into sugar and a few byproducts, and one of our current best guesses for what causes hangovers is a chemical called acetaldehyde, one of those ethanol byproducts.  When we try to block the metabolism of acetaldehyde using drugs, symptoms get worse.  This implies the higher the concentration of acetaldehyde in your body, the worse the symptoms, but even that's not entirely certain, because acetaldehyde is metabolized into acetate really quickly.

So in 2010, researchers tested ethanol and acetate separately in rats and tried to measure hangover-like headaches.  A few hours after giving the rats each substance, researchers applied different levels of pressure to the rats' heads and looked for some kind of response that indicated the rats felt the poke, and with both substances, it took less and less force to produce a headache, but as far as we can tell, no one's tried feeding acetate to humans yet.  With such a fuzzy understanding behind the cause of hangovers, you can imagine how hard it is to study, especially in people.

Research is often done by surveying people after a night of drinking and variables like how long participants drank and how strong their drinks were vary wildly between studies.  Plus, even controlled studies are rarely blinded.  It's theoretically possible, but beyond a certain amount of alcohol, participants generally know they're getting drunk.  

Even though hangovers are so hard to study, we can look into things that affect the hangover itself.  For instance, a common piece of advice says that you should never drink on an empty stomach, unless you want a hangover, and that's totally true.  In a classic 1994 study out of Sweden, researchers had ten men fast overnight, then gave them either a moderate dose of alcohol on an empty stomach or fed them a hardy breakfast along with it.  Sure enough, the participants who drank on an empty stomach felt drunker and had a higher blood alcohol concentration in the hours after drinking.  The breakfast group also cleared alcohol from their blood more quickly, suggesting that the presence of food sped up alcohol metabolism.

So make sure you have something in your stomach before drinking and while you're at it, make sure you avoid smoking, too.  I mean, that's just good advice in general.  Researchers writing in 2013 had college students keep a log of their alcohol and tobacco use for eight weeks alongside a record of their hangover symptoms.  Not surprisingly, hangover symptoms were the worst on Saturday and Sunday mornings, but they were also worse after smoking cigarettes, and the  number of cigarettes mattered.  As long as the participants drank above a certain number of alcohol, more smoking lent itself to more severe hangover symptoms on average, so even if you only smoke when you drink, you're still more likely to suffer the next morning.

The last thing that can make a hangover particularly nasty is the non-ethanol part of your drink, a group of chemicals called congeners.  These are things other than ethanol that are produced during beverage fermentation like acetone, tannins, and other chemicals, and drinks with more congeners have been shown to lead to worse hangovers.  For example, bourbon has a higher concentration of congeners than vodka.  Bourbon has also been shown to produce more severe hangovers than vodka, but the science is actually kind of mixed.  

For example, researchers in older studies had pointed to one particular congener: methanol, for hangover symptoms.  But more recent experiments have shown otherwise.  For example, a 2017 study showed that urine methanol concentration was not correlated with hangover severity.  We're talking self-reported hangover severity, mind you, so it's hard to measure anyway.  

So at the end of the day, to avoid a hangover, that common sense advice is the best we've got.  Skip cigarettes, not meals, or don't drink in the first place.  Otherwise, you might be in for one heck of a headache.

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