Why does alcohol make you pee more?

Ever wondered why you need to pee so much when you’ve been drinking?

For most people Glastonbury 2007 was all about mud, mayhem and Amy Winehouse messing up on the main stage. But Michael, a 31-year old Brighton-based computer programmer, has different memories – mainly involving the notorious festival toilets.

"By early evening on the Friday I'd already overdone it at the pear cider stand," he says. "So I spent half the night staggering between the bar and the toilets. I reckon I saw more of the portaloos than I did the bands!”

Diuretic dangers

You don't need to be a scientist to see the toilet queues at festivals or summer sporting events and make the link between drinking alcohol and the need to pee. So why does it sometimes seem like we spend more time queuing for smelly portaloos than soaking up the sun?

“Alcohol is a diuretic,” says Professor Oliver James, head of clinical medical sciences at Newcastle University. “It acts on the kidneys to make you pee out much more than you take in – which is why you need to go to the toilet so often when you drink.” (1) In fact for every 1g of alcohol drunk, urine excretion increases by 10ml.(2)

Alcohol also reduces the production of a hormone called vasopressin, which tells your kidneys to reabsorb water rather than flush it out through the bladder. With the body's natural signal switched off the bladder is free to fill up with fluid, making the toilets suddenly more appealing than your favourite band.

Breaking the seal

A common side effect of drinking is needing the toilet just five minutes after your last visit. This irritating experience (usually known as 'breaking the seal') happens because alcohol delivers a hefty double whammy to your kidneys.

"Suppose you have a pint at lunchtime," explains Oliver James. "At some point you'll need to go to the toilet and get rid of the pint of liquid you've just drunk. Then an hour later you'll have to pee again because of the added diuretic effect."

So won't weeing the alcohol out of your system help with next day's hangover? Unfortunately not.  Because alcohol promotes peeing, it can lead to dehydration, which causes the nausea and headache associated with bad hangovers. It's also why your mouth might feel like the driest place on earth. 

Switching to shorts won't stem the flow either, since whether you're downing pints or doing shots, it's the diuretic element of the alcohol which is key to producing all that wee.  

Tackling dehydration

With fluid leaving your body so quickly, dehydration can be a big problem. The signs of serious dehydration can include dizziness, confusion and tiredness, so it can be difficult for festival or sporting event stewards to tell if someone is just drunk, or in real danger. (3)

The best way to avoid dehydration from alcohol is to stay within the recommended limits. If you are drinking alcohol, always make sure you stay topped up with water throughout the day. If buying water around the festival site seems expensive, take a big bottle with you and fill up from the main pumps.

Spending time with friends in the great outdoors or sharing a brilliant day of sport can be magic. So go easy on the alcohol and get stuck into the action, rather than the toilets.

(1) Interview with Oliver James
(2) (1) Eggleton MG. The diuretic action of alcohol in man. J Physiol 1942;101:172-191
(3) See NHS Choices pages on dehydration