causes of hangover symptoms

Evidence based

Why Does Alcohol Cause Hangovers?

Afterdrink Author Dewey Jhon
Dewey Jhon


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  1. This article is based on currently available scientific evidence at the time of writing and fact checked.
  2. All referenced studies and research papers are from reputable and relevant peer-reviewed journals or academic associations.
  3. Some peer-reviewed papers have stronger study designs and are more robust in terms of quality and reliability. We will make every effort to highlight weak evidence.
  4. This article contains scientific references. The numbers in the parentheses (1, 2, 3) are clickable links to peer-reviewed scientific papers.
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Evidence based

By definition, a hangover is a culmination of symptoms which starts when the blood alcohol levels start to drop and is at its peak when the alcohol level reaches zero. Typical hangover symptoms include:

  • Headache
  • nausea & vomiting
  • concentration problems
  • anxiety
  • dry mouth
  • dizziness
  • fatigue
  • sweating

But really it needs no introduction…

If you’ve ever experienced one, you know exactly what the symptoms are and how debilitating they can be.

If you’ve ever wondered what the science behind all these common symptoms are then this article  is for you.

Table of contents

1) Nausea & vomiting – The direct toxin effect to the stomach

Lets face it, alcohol is a toxin.

Alcohol is used in hand sanitiser to kill 99.99% of bugs. Its clearly not going to swoosh around in our stomachs and leave harmlessly like water.

Alcohol has a direct effect on the cells lining your stomach and intestine by causing irritation which leads to that well known queasy feeling the morning after a big night out.

As a result of the inflammation, your stomach produces more acid which explains why some of us get heartburn after drinking.

2) Hangover anxiety – The Fear!

Probably up there with one of the worst hangover symptoms – the fear.

The science behind this phenomenon is complicated but can be mainly explained as an “acute withdrawal syndrome”.

Essentially, when the alcohol levels start to drop, your brain is in a hyperactive state as its neurones have been suppressed the night before.

You can find out more about this in our article about hangover anxiety.

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3) The main damaging by-product: Acetaldehyde

Alcohol is broken down by the liver to produce a substance called acetaldehyde which is highly toxic and is responsible for headache, nausea and generally awful feeling that comes with a hangover.

Our livers can only break down acetaldehyde at a slow rate. So the more we drink the more acetaldehyde builds up.

Think of it this way:

Imagine your liver is a mailing company. It can only package and post one piece of mail every hour. If you start throwing lots of mail at the mailing company (tequila shots), you start to get a build up and eventually the poor person posting all the mail (your liver) becomes burnt out – hungover.

Acetaldehyde is one of the MAJOR causes of the hangover symptoms and it can be linked to all the main hangover symptoms we are familiar with.

4) Breaking the seal

Alcohol is a diuretic which means that it increases the amount of urine your kidneys produce. To put this into perspective, for every pint of beer, you lose an extra 280 millilitres of fluid.

Ever woken up in early hours of the morning with a mouth as dry as the sahara desert, desperate for water? Well its because of this well known fact.

Dehydration plays a huge role in our hangover symptoms and on its own can add to the feeling of being tired, lethargic and light headed.

5) Hangover effect of Congeners

Everyone knows that red wine or whisky hangovers are the worst hangovers in the world. This is because the darker drinks contain more congeners.

These bad boys are what is produced during the ageing process of some alcohols. Some drinks such as red wine, whisky and cognac are aged in barrels to add to their flavour, smell and appearance.

Lots of research studies have shown how darker drinks which have more congeners contribute to worse hangovers. Im sure we have all found this out ourselves the hard way ourselves…

6) Low blood sugar

Alcohol stops your liver from producing glucose which is the fuel your organs and most importantly your brain uses to produce energy.

Low blood sugar is particularly a problem when binge drinking and starving your brain of glucose can lead to fatigue, weakness, and mood disturbances

isaac newton

7) Sleep disturbance

Have you ever felt that you can never sleep past a certain time if you’ve been drinking the night before?

Because alcohol is a sedative, it dampens down your nervous system which is why you sleep so easily.

“For every action, there is an equal and opposite reaction”

Once your asleep and the alcohol levels drop in your blood stream you get a rebound activation of the brain excitation waves that spring your brain into an active state.

This explains why you may randomly wake up in the early hours of the morning after a big night out.

To add to this, alcohol disrupts the normal sleeping pattern by reducing the time spent in REM (rapid eye movement) sleep. This is the deep phase of sleep which is essential in helping you feel well rested.

8) How long do hangover symptoms last? – Genetics

Studies suggest that 75% of people who drink socially experience a hangover at least once a month.

yes thats right…

That means 25% don’t get hangovers at all and we all know someone like this!

The fact is, everyone reacts differently to alcohol and some people will always have worse hangovers that last for different amounts of time and this is down to our genetics.

In some people of oriental/asian origin, consuming small amounts of alcohol can lead to flushing of the cheeks, becoming sweaty and feeling nauseas. This is known as asian flush and is caused by a rapid build of acetaldehyde.

You can find out more about this in our article about how long hangovers last.

Cause of hangover symptom: Final words

The meaning of being hungover is unique to every individual and is caused by many different factors.

There is no real treatment for a hangover and how long a hangover lasts will depend.

There a definitely tips and tricks to help along the way but the best way to avoid a hangover is to drink slowly and in moderation.

For more information, check out our article on how to prevent a hangover.

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