Does drinking alcohol actually cause dehydration?


Today I came across this article: Drinking water doesn’t prevent a hangover, study says, which includes the memorable line: “[the] study concluded, the only way to prevent a hangover is to drink less alcohol.”

Now, at first sight, you might think that surely this simply another piece of work from the University of the Bleedin’ Obvious.

But hang on. Alcohol does dehydrate you, doesn’t it? Everyone knows that! After all, don’t you wee more when you go drinking, and wake up all sweaty and with a dry mouth after a ‘heavy night’? Surely this is all evidence of fluid loss? Am I really about to suggest we should consign ‘alcohol causes dehydration” to the collection of alcohol-based myths such as mixing drinks gives you a worse hangover (only if you drink more as a result), a night cap will help you sleep (only temporarily, overall it tends to disrupt sleep), drinking beer will cause a ‘beer belly’ (too much of any type of drink can cause weight gain), and so on?



There are many alcohols; ethanol is the one we drink.

Firstly, what is alcohol or, more specifically (the word ‘alcohol’ actually refers to a group of compounds), ethanol? It’s a simple molecule, containing only two carbon atoms, an oxygen and some hydrogen atoms. It’s produced, as we all learned at school (or possibly when attempting home-brewing), by yeast during the process of fermentation. Feed this clever little single-celled organism some sugar and voilà, it produces ethanol (C2H5OH) and carbon dioxide via a remarkably simple equation:

C6H12O6 –> 2C2H5OH + 2CO2


Marula fruit naturally ferments.

Humans learned this trick a long time ago and have been brewing for literally thousands of years. In fact it doesn’t even require human intervention – marlula fruit is particularly famous for becoming naturally alcoholic (although stories of monkeys and elephants using it to get drunk might be somewhat exaggerated).

We like drinking because, of course, of what it does to us. In medical terms, it’s a central nervous system depressant with significant psychoactive effects (sounds fun, eh?) In English, it reduces anxiety, making drinkers feel relaxed and happy. This accompanies a decrease in motor skills of course, which is why drinking and driving is illegal virtually everywhere (although exact definitions of what this means do vary).

But while alcohol is all natural, it’s not what you’d consider healthy. Every now and then someone drags out some data that suggests that low to moderate alcohol intake is good for you, but this sadly appears to be more wishful thinking than good science. In terms of disease, alcohol consumption has been linked with stroke, high blood pressure, several liver diseases, pancreatitis, a weakened immune system and a handful of cancers including mouth, throat, liver and breast cancers.

In fact, alcohol has been categorised by the International Agency for Research on Cancer as a group 1 carcinogen, which puts it in the company of such other delights as asbestos, radium isotopes, ultraviolet radiation, diesel exhaust and tobacco.


Give up alcohol before you worry about your latte ingredients.

Of course, the dose makes the poison. Lots of people enjoy low to moderate alcohol consumption quite safely. Still, I have to admit to being amused by health nuts that insist on a diet consisting of little more than raw vegetables, make a fuss about so-called GMOs, campaign for additives (none of which are anywhere close to being group 1 carcinogens) to be removed from food, and then post pictures of themselves drinking wine. You really want to improve your health? Never mind caramel colour IV in your latte, give up the booze.

So, alcohol isn’t a health food, or indeed drink. But to get back to the original question, does it cause dehydration? Well, it would appear that while it does do a lot of bad stuff health-wise, that’s not one of the bad things it does. In a study, men drank six pints of beer and were then subjected to a number of tests. As the subsequent PubMed article states: “All subjects had a slight hangover, but none was fluid depleted”.

Screen Shot 2015-08-29 at 18.22.08

Twin doctors Chris and Xand van Tulleken in a recent BBC documentary.

In a recent BBC Horizon documentary, twin doctors Chris and Xand van Tulleken collected all their urine during a night in which Xand drank 21 units of alcohol in one sitting (while his brother only had one drink), and next morning demonstrated that the volumes were the same. In other words, the excessive alcohol consumption had not, as is widely believed, had a significant diuretic effect.

Admittedly, this was only two people, and the PubMed study only involved six participants – small sample size is often an issue with such work. The Dutch study I mentioned at the start was much larger, which is one reason it’s useful. In that study, drinking water appeared to make little difference to the severity of the hangover experienced. The only thing that really mattered was, not surprisingly, how much alcohol had been consumed.

In fact it’s not well-understood what does cause hangovers. It would appear it’s linked to an immune system response. In very simple terms, getting blind drunk is a little like self-imposed flu. Drinking plenty of fluids won’t do you any harm, but it’s not actually a solution. Of course, there’s no virus involved here to keep the immune system on the warpath, so for most healthy people the best, and probably only, hangover cure is time.

So in summary, yes, we probably can chuck “alcohol causes dehydration” in with all the other alcohol myths floating around out there, but that’s not an excuse to have a pint after your workout.

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39 thoughts on “Does drinking alcohol actually cause dehydration?

  1. Pingback: Everything you’ll ever need to know about hangovers | Vus Times

  2. Pingback: Press Today » Everything you’ll ever need to know about hangovers

  3. Sorry to be that guy, but the study you mentioned is clearly poorly executed. Like every good drunk, I know that even after one shot I can piss out a whole lot of very clear urine. What I’m saying is that there was no control group, if there was nobody who did not drink.


    • You can probably pee out a load of clear urine without drinking a shot: your bladder refills all the time 🙂 I appreciate that a sample size of two isn’t flawless science, but for the me the TV programme where identical twin brothers (who are also doctors) went out drinking and measured all the fluid in and all the fluid out was certainly enough to cast serious doubt on the dehydration issue. You’d assume, if it’s so clearcut, that the one drinking alcohol would pee out more compared with what he consumed. But no. Basically output matched input, for both. He had a hangover, but there was no evidence of dehydration. In the bigger study, well actually, dehydration can be measured objectively. It’s just a question of looking at ion concentration. So a control for that particular measure may not be essential


    • you conclude.. “we probably can chuck alcohol causes dehydration ” in a 2 person study??? we all KNOW that drinking alcohol dehydrates.


      • Ah well, if “well all KNOW it” then it must be true… right?

        Once upon a time everyone KNEW the sun orbited the Earth… except it doesn’t. And everyone KNEW that stomach ulcers were caused by diet and lifestyle… until Barry Marshall proved that most of the time they were actually caused by bacteria. And umpteen examples in between. Sometimes the accepted wisdom turns out to not be very wise.

        For more on alcohol not causing significant dehydration, see This is admittedly another small study, but it shows the same result. Also is a review of a number of trials which concluded that nothing helps a hangovers, other than prevention. If dehydration were the cause of the discomfort you’d expect that drinking water would reduce hangover symptoms, but it doesn’t.


  4. What about all the info that shows it suppresses Vasopressin, which which makes you pee about another 100mL per drink?
    Do you think this is wrong?


    • Well, it would appear that there’s also evidence that individuals drinking alcoholic drinks don’t actually excrete more urine than those drinking non-alcoholic drinks. So… further research is probably needed. That’s what science is all about: if you get a result that doesn’t appear to match your existing models, you either have to figure out what went wrong with that result, or you have to change your models.


    • No, it’s inflammation caused largely by acetaldehyde (ethanal), which is toxic, and carcinogenic. Alcohol breaks down into acetaldehyde, then forms acetic acid before going on to produce acetyl coenzyme A. Glucose (which I assume is what you mean by sugar?) isn’t directly involved.


    • That’s a link to the website for Gastrolyte rehydration tablets and other products. They’ve quoted no references. Do you think they might have a small interest in convincing people they’re dehydrated, given that they’re selling a product which is intended to fix that problem?


  5. I know this is n=1 and therefore nonscientific, but alcohol ABSOLUTELY dehydrates me, and severely – even just one or two drinks (although my preferred amount is 4-8 depending on the night). Each time I drink, it legitimately takes a full day of fluid intake to reach non-dehydrated levels. My urine is very, very concentrated and yellow the next day, and I can drink copious amounts of water (the next day) without peeing – these are both signs of dehydration. In addition, if I go for a run or other physical activity, I tire quickly and feel physical symptoms of being dehydrated.

    Oh, how I envy those doctors whose body chemistry allows them to drink without becoming dehydrated.


    • It wasn’t just the doctors, it was a large number of study participants as well. It’d be interesting to see if your electrolyte balance reflected you perception that you’re dehydrated.


      • I believe when I drink only 2 pints of lager, it causes some level of dehydration. Mouth feels dry the next day and also I am a couple of pounds lighter on the scales. Then because my body is dehydrated, I suffer from water retention that lasts a couple of days before the body flushes out the excess water resulting in a night of having to get up about 5 times.


      • I’m not sure that really proves anything… although I think if you’re having to get up 5 times on a regular basis, you might want to get checked out by a doctor.


  6. Pingback: Dehydration: Do You Know The Dangers - VetBest Health

  7. Study size of 2 and 6. Impressive data you have collected there lol. If you are going to spend this amount of time writing a blog at least try and make it have some slight methodological rigour


    • There was more to the post than just those two things. Also, did you look at the other studies I mentioned? There’s one with 5459 participants, and other follow-up with 789. In particular, there’s a Dutch study with 826 participants which concluded that “consuming food or drinking water, either before going to bed or during hangover, ha[s] no relevant effect on the severity of alcohol hangover”. See and


      • I was being a little facetious and yes the other studies sound far more convincing perhaps you could have made this clearer . However I don’t think you can just dismiss the other evidence particularly the number of studies conducted on rats indicating significant electrolyte imbalances and dehydration caused by administering alcohol and the basic empirical evidence that millions will surely attest to that a fry up and drinking water makes a hangover far less severe . I’m not an academic I’m a nurse although I completed post grad research training in a previous life. However of the articles I’ve just read it seems yes alcohol does not directly cause dehydration however it has significant effects on our immune system which then do cause symptoms of dehydration and loss of electrolytes common sense tells us from this drinking water/electrolyte solution is probably going to help you feel a bit better regardless of whether it ‘cures’ your hangover or not. Carry on the good work I do miss a good debate


      • Thanks! 🙂 But there’s the thing: it doesn’t directly cause dehydration. Dehydration-like symptoms aren’t quite the same thing. Look up alcohol pretty much anywhere other than this blog and one of the first things you’ll see is “it dehydrates you”.


      • Yes I agree if I was to give constructive feedback I would just say your conclusion could have been more nuanced. Anyway I’m off out now nice talking to you


  8. Ok so this all makes sense, however the fact I see that has not been considered is the obvious and that is by having a glass of water between alcoholic drinks it slows down the rate in which one drinks the alcohol. So drinking a glass of water for every glass of alcohol won’t help you beat the hangover through supplying your body with more water and therefore avoiding dehydration but it will help you by slowing down the amount of alcohol actually consumed. Therefore reducing the effect of a hangover. In conclusion water does not help itself but the action of stopping consuming alcohol to consuming water does in fact reduce the affect of a the morning after feeling!


  9. This is ridiculous. We all know that there is a direct correlation between alcohol and dehydration. You don’t need to scientifically dissect this, all you need to do is use your previous experience to know this. When you consume a good nights amount of alcohol and wake up with cotton mouth and your lips get chapped, that’s an obvious sign of dehydration… who doesn’t know this??


    • This is exactly what scientists DON’T do. If we relied on things being “obvious” we’d still think the sun goes around the Earth, illnesses are caused by bad smells and fire is a chemical element. The evidence doesn’t support the idea that the symptoms you describe are actually due to dehydration.

      Liked by 1 person

  10. How do you arrive at that summary? Seems like all you’re pointing to is a study by two guys, and an article which is about a separate topic (drinking water to avoid a hang over).

    I’m pretty convinced from personal experience that when I drink hard alcohol (tequila, vodka), my body gets seriously dehydrated and my muscles get tight, and I even think that my spinal disc could have dehydrated and lost some load-carrying capacity after a heavy night of drinking, making it more susceptible to herniating. I’m an engineer not a doctor though 😛


    • I think I made it fairly clear how I reached my conclusion – third paragraph from the bottom. Yes, sample sizes are small, but nevertheless – where people have studied this, the evidence that actual dehydration is happening just isn’t there. Yes, there are symptoms which seem to be SIMILAR to those that cause dehydration, but dehydration doesn’t seem to be the true cause of those symptoms.

      If you know of any studies – not just anecdotes – which prove that dehydration DOES occur, please tell us 🙂


  11. I agree with this. I used to exercise quite a bit and every time I was dehydrated I was several pounds lighter than my normal weight. Every time I’ve been hungover, I weigh the exact same as I normally do. I also know that drinking a ton of water and gatorade doesnt make me feel better like when I am really dehydrated. As for the cotton mouth, diabetics or those with elevated blood sugar often get cotton mouth even thought they are hydrated. Thanks for sharing the article. Im no scientist but from my own personal experience I’ve always doubted dehydration was the cause of a hangover.


  12. Alcohol may not cause dehydration, but surely causes symptoms (feelings) of dehydration in some people, including me. Drinking water may not prevent hangovers in the general population but it does for me. I always get a hangover when I don’t drink a lot of water after taking alcohol, maybe it’s psychological but doesn’t make it any less relevant, the feeling is real. This is the problem with thinking a research finding based on population means applies to every individual in the same way. Drinking water may not be helpful in preventing hangovers for a majority of the population but doesn’t mean it doesn’t help any individual, this is not Newtonian mechanics.


    • Drinking water may not prevent a hangover, but the unpleasant hangover symptoms are largely caused by the formation of (toxic) acetaldehyde as alcohol is metabolised. Drinking water may help to speed up the breakdown of that substance (into acetate, aka ethanoate) and then help with excretion. So whilst it won’t prevent the poisoning (because that’s what it is) it might help you recover a little bit quicker. BUT not because you were dehydrated.

      Liked by 1 person

      • You quoted a research paper that says drinking water does not prevent hangover, it does for me. Alcohol does not cause dehydration but can cause feelings associated with dehydration which was my point.


  13. As someone seriously trying to cut down on the basis of being told by quite a few medical persons that many of my health problems are down to dehydration caused by over indulgence then I’m totally and absolutely lost after reading your comments. Not for one minute am I disputing them..I’m just confused!


    • You should always take the advice of your doctors 🙂 Whether it causes dehydration or not, alcohol is definitely harmful. In your body it forms acetaldehyde, which is really toxic. That’s why it’s linked to so many cancers, and why it’s so hard on your liver. So cutting down, or even stopping all together, is generally good advice.


      • Thank you K..oh yeah was cutting down for all the usual reasons, funnily enough nothing to do with hangovers. I feel thats very much a “big hitter” type thing. Still persuing my goals, thankyou for your input.


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