Alcohol, dehydration and hangovers: what helps

2026-10-30

Yes, alcohol can dehydrate you, but less than most people think, and dehydration is only one part of a hangover. Alcohol suppresses vasopressin, the hormone that tells your kidneys to keep water, so you pee more than you otherwise would. The effect is clearest with stronger drinks like wine and spirits; ordinary beer barely differs from water in the studies that have tested it. Drinking water alongside alcohol helps with thirst and dry mouth, but no amount of water, coffee or electrolytes cures a hangover. Only drinking less, and time, does that.

How alcohol makes you lose water

Normally, when your body needs to hold on to fluid, your brain releases vasopressin (also called antidiuretic hormone). It tells your kidneys to put water back into the blood instead of sending it to the bladder. According to the US National Institute on Alcohol Abuse and Alcoholism (NIAAA), alcohol suppresses the release of vasopressin, so the kidneys let more water go. The NIAAA says the resulting mild dehydration likely contributes to hangover thirst, fatigue and headache.

That's why a night out often comes with frequent trips to the toilet and a dry mouth the next morning.

Does it depend on what you drink?

Yes. The amount of alcohol per glass matters more than the type of drink.

Beer. In a 2016 trial that compared the urine output after one liter of various drinks, a regular lager produced the same amount of urine over four hours as still water. A 2017 crossover trial in older men found no difference between regular and alcohol-free beer at any point.
Wine and spirits. In that same 2017 trial, moderate amounts of wine and spirits (30 g of alcohol in total) increased urine output during the first four hours compared with their alcohol-free versions and water. By 24 hours, the difference had disappeared. The authors described it as a short, small diuretic effect.

Both studies were small and used moderate amounts. Heavy drinking is a different story: more alcohol means a stronger, longer effect, and vomiting or sweating in a hot club adds to the fluid loss.

Dehydration is not the whole hangover

A hangover is more than thirst. The NIAAA lists several other contributors:

Poor sleep. Alcohol may help you fall asleep but disrupts sleep later in the night.
Stomach irritation. Alcohol increases stomach acid and can cause nausea and pain.
Inflammation and the effects of acetaldehyde, a toxic by-product of breaking down alcohol.
Mini-withdrawal. As the buzz wears off, some people feel anxious or restless.
Congeners. Darker drinks such as bourbon contain more of these fermentation by-products, which may make hangovers worse for some people.

According to the NIAAA, symptoms peak when blood alcohol returns to about zero and can last 24 hours or more. That's why rehydrating helps with the dry mouth and some of the headache, but doesn't make you feel fine.

What actually helps

Before and during drinking

Eat first. Food slows how fast alcohol is absorbed.
Alternate with water. A glass of water between alcoholic drinks slows your pace and adds fluid. This is the single most practical habit, mainly because it means you drink less alcohol.
Pick lower-strength drinks. Lighter beer or a spritzer means less alcohol per glass, which matters more than anything you drink afterwards.
Set a limit before you start. Deciding on a number in advance is easier than deciding after the third drink.
Have water before bed. A glass of water at the end of the night, and one on the nightstand, helps with thirst and dry mouth. Don't overdo it: a liter at 2 a.m. will just wake you up again. (More on that in drinking water before bed.)

The morning after

Drink water steadily. Sip regularly rather than forcing down a large amount at once, especially if you feel queasy.
Eat something bland. Toast, crackers or soup can be easier on an irritated stomach.
Rest. Time is the only thing that reliably ends a hangover.
Be careful with painkillers. The NIAAA warns that acetaminophen (paracetamol) combined with alcohol can be toxic to the liver, and that aspirin and ibuprofen can irritate the stomach. If in doubt, ask a pharmacist.

What doesn't help

"Hair of the dog." Another drink may mask symptoms briefly but can prolong the hangover.
Coffee or a cold shower. They may make you feel more alert, but they don't speed up recovery. Coffee won't dehydrate you either (see does coffee dehydrate you), it just doesn't fix anything.
Electrolyte drinks and IV drips. The NIAAA notes that research hasn't found a link between electrolyte levels and hangover severity. Sports drinks or rehydration sachets are fine if they help you get fluid down, but they're not a cure. If you've been vomiting a lot, an oral rehydration solution makes sense; see electrolytes: when you actually need them.
Drink order. "Beer before wine" is a myth. The total amount of alcohol is what counts.
Sobering up with water. Water doesn't lower your blood alcohol. Only time does. Never drive the morning after a heavy night just because you feel "rehydrated".

When to get help

Severe vomiting, confusion, very slow or irregular breathing, seizures or being hard to wake are signs of alcohol poisoning, not a bad hangover. Call emergency services. And if you're unsure whether you're simply thirsty or properly dehydrated, check the signs of dehydration.

If you take medication, are pregnant, or have liver, kidney or heart disease, talk to your doctor about alcohol in general, not just about hydration.

Making the water part easier

The water-between-drinks habit is easy to forget once the evening gets going. A few things help: order a water with every round, keep a bottle in your bag, and log glasses as you go. With Water Tracker on an Apple Watch, logging a glass is a turn of the Digital Crown and a tap, without getting your phone out. The next day, the reminders nudge you to keep sipping, then go quiet once you hit your goal.

Bottom line

Alcohol makes you lose more water by suppressing vasopressin, and the effect is stronger with wine and spirits than with ordinary beer. Mild dehydration contributes to hangover thirst and headache, but poor sleep, stomach irritation, inflammation and acetaldehyde play a big part too. Eat first, alternate alcoholic drinks with water, choose lower-strength drinks and have a glass of water before bed. Nothing cures a hangover except time, and drinking less is the only reliable prevention.

This article is general information, not medical advice. If you have a health condition, are pregnant or take medication, ask your doctor how much you should drink.