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Short answer: Yes, alcohol can dehydrate you, but less than most people think at moderate amounts. Alcohol makes you urinate more by lowering vasopressin, a hormone that tells your kidneys to hold on to water. In controlled studies of about two drinks, the extra fluid loss was small and short-lived: results for beer were mixed, while wine and spirits caused a little extra urine that was gone within a day. Dehydration becomes more likely with heavier drinking, stronger drinks, vomiting, sweating or not drinking other fluids, and that mild dehydration likely adds to next-day thirst, fatigue and headache.
Waking up with a dry mouth and a headache after a night out makes it easy to blame dehydration. But how much fluid does alcohol actually take out of your body, and does the type of drink matter? Here is what controlled studies show, why alcohol makes you pee more, and practical ways to stay hydrated if you drink.
What you'll learn
- Why alcohol makes you urinate more
- Whether beer, wine and spirits dehydrate you differently
- How much dehydration contributes to a hangover
- Signs of dehydration to watch for
- Simple ways to stay hydrated when you drink
Does alcohol dehydrate you?
It can. Alcohol increases urination and fluid loss, and the mild dehydration that follows likely contributes to hangover symptoms such as thirst, fatigue and headache (NIAAA). How much it matters depends on how much you drink, how strong the drinks are and what else is going on. In studies of moderate amounts, the extra fluid loss was small and short-lived (Polhuis et al., 2017). After a long night of heavy drinking, especially with vomiting, sweating or little water, the effect adds up.
Why does alcohol dehydrate you?
Your brain releases a hormone called vasopressin that signals your kidneys to hold on to fluid. Alcohol suppresses vasopressin, so your kidneys let more water go and you urinate more (NIAAA). Researchers note that the full mechanism is not settled, because some studies did not find differences in vasopressin after alcoholic and non-alcoholic drinks, suggesting other factors may also be involved (Polhuis et al., 2017).
A widely repeated figure says each 10 grams of alcohol produces an extra 100 mL of urine. That estimate dates to 1942 and was based on data from a single person (Polhuis et al., 2017), so it should not be treated as a rule.
Beer vs wine vs spirits: what studies show
Several controlled studies have compared alcoholic drinks with the same drink without alcohol, or with water:
| Study | What people drank | What happened to urine output |
|---|---|---|
| Polhuis et al., 2017 (19 men aged 60 to 75) | 30 g of alcohol, about 2 U.S. standard drinks, as 5% beer, red wine or spirits with a meal, compared with non-alcoholic beer, non-alcoholic wine or water | Beer: no difference from non-alcoholic beer. Wine and spirits: more urine over the first 4 hours, but no difference over 24 hours (Polhuis et al., 2017) |
| Maughan et al., 2016 (72 men) | 1 liter of lager compared with still water | No difference in urine output over 4 hours (Maughan et al., 2016) |
| Hobson & Maughan, 2010 (12 men) | 1 liter of 4% beer compared with alcohol-free beer, when well hydrated and when already mildly dehydrated | Well hydrated: about 1,280 vs 1,120 mL over 4 hours. Already dehydrated: no significant difference (Hobson & Maughan, 2010) |
| Shirreffs & Maughan, 1997 | Drinks with 0 to 4% alcohol after exercise in the heat | Up to 2% made no difference to rehydration. 4% drinks tended to slow recovery (Shirreffs & Maughan, 1997) |
Results for beer are mixed: two studies found no extra urine, while one found about 160 mL more over 4 hours in well-hydrated men. In the 2017 study, wine and spirits raised urine output compared with their alcohol-free versions while beer did not, although the study could not show a clear difference between the drink types themselves. In all of these studies the effect was modest and short-lived (Polhuis et al., 2017; Hobson & Maughan, 2010). Most of the studies were small and included only men, and the 2017 study was carried out by researchers from the Dutch Beer Institute (Polhuis et al., 2017). The standard drink math is ours: a U.S. standard drink has about 14 grams of alcohol (NIAAA).
None of this makes beer a good hydration drink. These studies looked at about two drinks. They do not apply to a night of many drinks, and the more you drink, the more other risks matter.
Is dehydration what causes a hangover?
Only partly. Mild dehydration likely contributes to thirst, fatigue and headache, but hangovers also involve poor sleep, stomach irritation, inflammation and acetaldehyde, a toxic byproduct of alcohol (NIAAA). A 2024 review concluded that dehydration after drinking is usually mild and short-lived, and that hangover and dehydration often occur together but are largely independent. Drinking water during or after alcohol had only a modest effect on next-day hangover (Mackus et al., 2024).
So water helps you feel less thirsty and replaces what you lost, but it will not prevent a hangover on its own. See how long a hangover lasts and what helps.
Signs you may be dehydrated
Signs of mild to moderate dehydration include (MedlinePlus):
- Thirst
- A dry or sticky mouth
- Urinating less than usual
- Darker yellow urine
- Headache
- Muscle cramps
Vomiting, diarrhea and heavy sweating all add to fluid loss, and older adults are at higher risk of dehydration (MedlinePlus). Dancing in a hot room or drinking in the sun on top of alcohol makes losing fluid more likely.
How to stay hydrated when you drink
- Alternate drinks. Have a glass of water or an alcohol-free drink between alcoholic ones. It also slows how fast you drink. Try our easy mocktail recipes.
- Choose lower-strength drinks and smaller pours. In one study, wine and spirits raised urine output compared with alcohol-free versions while beer did not (Polhuis et al., 2017). Count drinks using the 14-gram standard drink (NIAAA).
- Eat a meal. Food adds fluid and helps you pace yourself. For the morning after, see our guide to the best food for a hangover.
- Drink water before bed and in the morning. It replaces lost fluid, even though it will not cure a hangover (Mackus et al., 2024).
- Skip the electrolyte hype. Research has not found a link between electrolyte changes and how bad a hangover is, and the body usually restores its electrolyte balance quickly (NIAAA). Water, broth or food are fine for most people.
- If you are nauseous, sip small amounts of clear liquids often instead of drinking a lot at once (MedlinePlus).
When to get help
Get medical care if you cannot keep fluids down for 12 hours or more, or have not urinated for 8 hours or more (MedlinePlus). Call 911 if someone loses consciousness, becomes confused or has a seizure, or shows signs of heatstroke such as a rapid pulse or rapid breathing (MedlinePlus).
After heavy drinking, also call 911 if someone cannot stay awake, is vomiting while drowsy, has slow or irregular breathing, or has clammy, pale or bluish skin. These are signs of alcohol overdose, and water will not fix them (NIAAA). See how to sober up and help a friend who drank too much.
Common myths (quick reality check)
Myth: Every drink makes you lose more water than it contains. Reality: This idea comes from a 1942 estimate based on one person. In controlled studies of about two drinks, the extra urine was modest and short-lived.
Myth: Dehydration is the main cause of hangovers. Reality: Dehydration is only one part. A 2024 review found hangover and dehydration often occur together but are largely independent, and drinking water had only a modest effect on hangover.
Myth: You need electrolyte drinks after drinking. Reality: Research has not linked electrolyte changes to hangover severity, and the body usually restores its electrolyte balance quickly. Water and food are enough for most people.
Frequently asked questions (FAQ)
Does alcohol dehydrate you?
Yes, it can. Alcohol suppresses vasopressin, a hormone that helps your kidneys hold on to water, so you urinate more. At moderate amounts the extra fluid loss is small and short-lived, but it adds up with heavy drinking, vomiting or sweating.
Why does alcohol make you pee so much?
Alcohol lowers vasopressin, the hormone that tells your kidneys to retain fluid. You also take in a lot of liquid when you drink beer or mixed drinks.
Does beer dehydrate you?
Only a little, if at all, in moderate amounts. Two studies found no extra urine after about two drinks' worth of beer, and one found about 160 mL more over 4 hours. Larger amounts are a different story.
Do wine and spirits dehydrate you more than beer?
In one study, the same amount of alcohol as wine or spirits caused more urine over the first 4 hours than non-alcoholic versions, while beer did not. The study could not show a clear difference between the drink types themselves, and the extra urine was gone after 24 hours.
How much water should I drink when drinking alcohol?
There is no proven ratio. A simple approach is to have a glass of water or an alcohol-free drink between alcoholic drinks and another before bed.
Does drinking water prevent a hangover?
Not on its own. Water replaces lost fluid and eases thirst, but a 2024 review found it had only a modest effect on next-day hangover.
What are signs of dehydration after drinking?
Thirst, a dry or sticky mouth, urinating less, darker yellow urine, headache and muscle cramps. Get medical care if you cannot keep fluids down or have not urinated for 8 hours or more.
Related guides
- Best food for a hangover: what to eat and drink
- How long does a hangover last?
- How long does alcohol stay in your system?
- Alcohol tolerance: what it is and why yours may be low
- How to sober up: what works and what doesn't
- Easy mocktail recipes
Disclaimer and when to seek help
This article is for general education and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Our products are not intended to diagnose, treat, cure, or prevent any disease. Call 911 for signs of alcohol poisoning or severe dehydration. Talk to your health care provider if you take medication, have a medical condition, are pregnant or breastfeeding, or are concerned about your drinking.
References
- National Institute on Alcohol Abuse and Alcoholism. "Hangovers".
- Polhuis KCMM, et al. "The diuretic action of weak and strong alcoholic beverages in elderly men: a randomized diet-controlled crossover trial." Nutrients, 2017;9(7):660. doi:10.3390/nu9070660
- Maughan RJ, et al. "A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index." The American Journal of Clinical Nutrition, 2016;103(3):717-723. doi:10.3945/ajcn.115.114769
- Hobson RM, Maughan RJ. "Hydration status and the diuretic action of a small dose of alcohol." Alcohol and Alcoholism, 2010;45(4):366-373. doi:10.1093/alcalc/agq029
- Shirreffs SM, Maughan RJ. "Restoration of fluid balance after exercise-induced dehydration: effects of alcohol consumption." Journal of Applied Physiology, 1997;83(4):1152-1158. doi:10.1152/jappl.1997.83.4.1152
- Mackus M, Stock AK, Garssen J, Scholey A, Verster JC. "Alcohol hangover versus dehydration revisited: the effect of drinking water to prevent or alleviate the alcohol hangover." Alcohol, 2024;121:9-18. doi:10.1016/j.alcohol.2024.07.006
- MedlinePlus Medical Encyclopedia. "Dehydration". U.S. National Library of Medicine.
- MedlinePlus Medical Encyclopedia. "Nausea and vomiting - adults". U.S. National Library of Medicine.
- National Institute on Alcohol Abuse and Alcoholism. "Understanding the Dangers of Alcohol Overdose".
- National Institute on Alcohol Abuse and Alcoholism. "What Is A Standard Drink?".
