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The Chemistry of a Hangover

Man with a bottle of alcohol leans over a table.

Man with a bottle of alcohol leans over a table.

If you’ve ever woken up the day after drinking and felt incapable of getting out of bed, a pounding headache, or that terrible churning feeling in your stomach, you’ve probably experienced a hangover.

Many people get hangovers, but few really understand the biological processes that cause them.

So what’s the chemistry of a hangover, exactly?

The chemical makeup of alcohol varies, so explaining a hangover is a bit complicated. You also need to consider what you’re mixing with your alcohol, what you drank the day before, and how your body processes all that.

It’s so complex that even scientists still don’t completely understand what truly causes hangovers. However, they’ve got some ideas.

1. Dehydration

The first theory to explain hangovers has to do with dehydration. Ever had to go to the bathroom a lot more than usual while you were sipping on drinks at a party? There’s a reason for that.

Alcohol is a diuretic. This means it creates more urine than say, a glass of water. More urine means your kidneys fill up faster, which means you also have to go to the bathroom more. In the process, you lose a lot of water. Hence, dehydration.

Dehydration can cause headaches, but studies haven’t proven that this is what causes hangovers, in general. So something else must be going on.

2. Alcohol affects your immune system

One way hangovers might occur has to do with the way alcohol affects your stomach and intestines. Your immune system kicks into action when you drink to fight off toxins in alcohol.

In the process, it causes inflammation in your stomach lining. This actually slows digestion and creates a buildup of gastric acid. In the end, you’ll feel nauseous, which is one aspect of a hangover.

The immune system reacts in other ways as well. When you drink too much, it releases molecules called cytokines. They are great if you’re trying to fight off an infection, but when they’re triggered by alcohol intake, they cause symptoms related to hangovers like muscle aches and even irritation.

3. As you process alcohol, an enzyme called acetaldehyde builds up in your body

Alcohol has ethanol. It’s toxic, so your body has to break it down and process it in the liver. This process isn’t very straightforward and involves a lot of steps.

Basically, the liver needs to convert ethanol to other substances in order to get them out of your body. One way this works is with an oxidizing agent called nicotinamide adenine dinucleotide or NAD+ and enzymes called alcohol dehydrogenase or ADH.

First, NAD+ and ADH work to change ethanol to acetaldehyde. This is still toxic though, so another enzyme changes it to acetic acid.

Now, your body can get rid of all those toxins. However, your body can only handle so much alcohol at once.

When you drink in excess, your liver can’t properly process acetaldehyde. If it builds up, it can actually enter your blood stream. Since it’s more toxic than ethanol, it could cause a lot of the problems associated with hangovers.

This also explains why some people get “drunk” more quickly. People of East Asian descent often can’t tolerate much alcohol because their bodies end up converting ethanol into acetaldehyde too fast.

Then, that acetaldehyde builds up faster than they can turn it into the harmless acetic acid.

Actually, the connection between unpleasant feelings and drinking is so strongly associated with acetaldehyde some use it to help treat alcoholism.

Scientists developed a drug called Antabuse. It effect, it stops the liver from processing nausea and headache inducing acetaldehyde.

This can be especially helpful for people trying to stop drinking because it makes them feel worse when they drink. If they feel worse, they’ll want to drink less.

4. Some drinks are more likely to cause hangovers than others

Not all drinks are created equally. Different types of alcohol have varying levels of congeners, chemicals that are made during fermentation.

Different methods of fermentation produce different levels of congeners. For example, beer has fewer congeners than wine or brandy, which have some of the highest levels.

Some of these congeners, like methanol, stay in your body, even after you’ve processed all the ethanol. Studies show alcohol that has higher levels of congeners generally increases your risk for developing a hangover.


Alcohol is complex, and so is your body. Whether or not you get a hangover depends on many factors, but there’s one sure way to prevent it – don’t drink in the first place.

However, if you are going to drink, drink less and pace yourself. It helps to intersperse your alcoholic drinks with something else, like a glass of water. You should also make sure to eat while you drink to slow the alcohol absorption.

Other than that, however, there’s probably no secret way to cure a hangover. Really, the best thing you can do is to avoid alcohol altogether or at least drink responsibly.

If you find that you aren’t really able to control how much you drink, you may have an addiction to alcohol. In this case, simply saying no or “pacing yourself” isn’t possible. In order to regain control of your life and stop drinking, consider treatment and speaking with a healthcare professional.