does alcohol dehydrate you

Evidence based

Why Does Alcohol Dehydrate You?

Afterdrink Author Kathy Caldwell
Kathy Caldwell


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  1. This article is based on currently available scientific evidence at the time of writing and fact checked.
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Evidence based

It’s early in the morning and you’ve woken with a dry mouth like the Sahara desert and desperate for a jug of water.

Sound familiar?

We all know that alcohol dehydrates you and that it’s one of the main causes of a hangover.

But how exactly does it dehydrate you?

In this article, we’re going to take a closer look at the science behind alcohol and dehydration. We will also give some tips to get you back on your feet after a big night out.

Table of contents

Sings and symptoms of Dehydration

The signs and symptoms of dehydration can be split into two categories. You’ll probably be familiar with many of them already but there are some really important ones to look out for.

Symptoms related to fluid loss:

Most of the symptoms related to dehydration can be attributed to “volume depletion”.

You have just over 5 liters of blood in your vascular system (depending on how big or small you are) which transports nutrients around your body.

When you’re dehydrated, your body does everything possible to keep this volume stable as its the most important thing for keeping you alive.

As a result, fluid is extracted from your cells to maintain the blood volume.

Eventually, if dehydration becomes very severe, you start to lose water from your blood. The most common symptoms of all this include:

  • Dizziness
    – especially when going from a sitting to a standing position
  • Dry mouth
  • Muscle aches/cramps
  • Low energy
  • Reduced urine production
    – Your kidneys try to preserve as much fluid as possible leading to dark colored urine.

Symptoms related to electrolyte disturbance:

Your kidneys control the balance of your electrolytes. They do this by adjusting how much is preserved and how much is allowed to leave.

By electrolytes, we mainly mean sodium, potassium, phosphate, and calcium.

When dehydration becomes severe, the kidney prioritizes water above all else which can lead to fluctuations in the electrolyte balance.

Your body normally has very tight control of your electrolytes and even small deviations can cause symptoms such as:

  • Confusion
  • Muscle twitching
  • Increased breathing rate
  • Seizure

Of course, these are extremely unlikely to occur after a night of drinking alcohol. But we thought we’d cover the range of symptoms that can happen from mild to severe to that you can spot the signs early.

The first symptoms of dehydration are dry mouth and lethargy but in severe

How does alcohol dehydrate you?

Alcohol blocks the production of a hormone in your brain called anti-diuretic hormone (ADH).

This hormone is responsible for reabsorption of water from your kidneys.

Therefore blocking its production causes you to lose more fluid.

It’s as simple as that really.

This is why alcohol is a “diuretic” which means it makes you pee more fluid than you are consuming.

How much does alcohol dehydrate you?

There are a few studies that have looked at alcohol and its diuretic effect.

Generally speaking, 1 unit of alcohol makes you urinate around 120ml of extra fluid.

1 unit is equivalent to 1 standard shot of 40% spirit.

So a double vodka lemonade will be 2 units and you’ll lose 240ml of fluid.

If you were to drink a pint of beer which is around 2.2 units (Depending on strength of the beer) – you’ll lose around 260ml of extra fluid.

You get the drift…

The total amount of alcohol you consume will determine how much fluid loss there is over what type of alcohol is being consumed.

What if you switch to drinking alcohol with less volume?

It won’t make a difference if you only have shots or beer all night.

Even though one has much less volume than the other, the diuretic effect comes from the alcohol quantity.

If you drink beer all night you’ll need to go to the toilet a lot more often which is because of the volume of fluid in the beer.

But overall, the net loss of fluid will be the same as if you were only having tequila shots.

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Which alcohol is the worst for dehydration?

There’s no single type of alcohol that’s worse for dehydration than others.

The main factor is the number of units you drink which directly correlates to the strength of alcohol.

A shot of 74% absinth is more dehydrating than a shot of 40% tequila. That’s because a shot of absinthe has almost 2 units of alcohol.

How much water should you drink after alcohol?

Ok, so let’s say you had only had 5 tequila shots all night. That’s 5 units of alcohol.

So it means you’ll need to drink around 600ml of water to rehydrate yourself.

It’s important to note that these numbers are only rough estimates and everyone will experience different levels of dehydration after drinking alcohol.

Best way to rehydrate after drinking alcohol

The best way to rehydrate after drinking alcohol is to drink a glass of water between each drink.

This allows your body time to adjust for the fluid loss as well as more time to clear alcohol from your bloodstream between the time it takes to have your next drink.

Not only will this rehydrate you, but you’ll also have much less of a hangover the next day.

Another top tip is to have a rehydration sachet at the end of your night. These are usually used for people with diarrhea but they’re excellent for all dehydration purposes.

Rehydration sachets also contain essential minerals and salts which help replace what’s lost after drinking.

You’ll be able to find them over the counter in any pharmacy or food mall.

How long does it take to rehydrate after drinking alcohol?

This depends on how fast you can drink water.

We wouldn’t recommend trying to drink as much as you can in a short period of time.

If you’ve had a big night out and you’re hungover in the morning, it won’t be the best idea to down as much water as you possibly can.

Your stomach will be in a fragile state and any unnecessary pressure may make you feel more queasy.

Most people will attribute all their hangover symptoms on dehydration which is incorrect.

If you’ve drunk loads of water and still feel “dehydrated”, it’s more likely you’ve just got a bad hangover.

Dehydration and hangovers have different symptoms.

Fastest ways to rehydrate after alcohol

The fastest way to rehydrate after drinking alcohol is to get yourself on an IV drip.

This way you’ll be able to pump a liter of fluid straight into your circulation in less than an hour.

There are plenty of rehydration IV drip companies around that will be able to do this for you.

However, it’ll set you back a few hundred dollars – not cheap at all.

Also, it’s not ideal having to go through the hassle of having an IV drip every time you drink.

Drinking alcohol when dehydrated

Drinking alcohol when you’re already dehydrated after exercise is a big problem.

After exercise, your muscles will require water and energy to help restore and repair damaged cells.

Aside from the fact that alcohol will make you even more dehydrated, your body starts to use it as an energy source instead of carbohydrates and protein to rebuild muscle.

In fact, studies have shown alcohol to be damaging to muscle recovery after exercise.

Consuming alcohol after exercise will slow down muscle recovery and repair.

Anything else to consider?

Alcohol is a powerful diuretic and can cause dehydration over the course of your night out.

Each drink you have has an additional increase in the amount of fluid you’ll lose.

Add this up after a night of drinking and you’ll be guaranteed to end up dehydrated the next day.

Preventing dehydration is the most important thing you can do rather than trying to rehydrate yourself the next day by downing large amounts of water.

Limiting your alcohol intake and making sure you have plenty of water backed to balance out the losses is key to preventing dehydration and the worst hangovers.

Wrapping Things Up – Final Words

So, that brings us to the end of our look at alcohol and why it dehydrates you.

We’ve walked you through the science behind how it does so and covered tips on how to rehydrate yourself safely.

Always remember to drink a small glass of water between every one or two alcoholic drinks to prevent dehydration and bad hangovers.

Also, be sure to check out our article on how to rehydrate quickly after drinking alcohol.

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