Hangovers: how your body is affected

A hangover is the unpleasant consequence of having overindulged or had ‘one too many’ alcoholic drinks. Symptoms usually appear a few hours after stopping drinking, and may include:

  • headache;
  • nausea and vomiting;
  • diarrhoea;
  • disturbed sleep and fatigue;
  • anxiety and irritability;
  • decreased concentration;
  • tremor or shaking; and
  • sweating.

Doctors believe that there are many things that contribute to these unpleasant symptoms, including dehydration and the way alcohol is processed (metabolised) in your body - i.e. the way your liver breaks down alcohol.

Metabolism of alcohol

alcohol metabolism

Your liver processes alcohol in two steps. Firstly, an enzyme in your liver cells — alcohol dehydrogenase (ADH) — converts alcohol to a toxic substance called acetaldehyde. Acetaldehyde is then converted to acetate (a non-toxic substance) by another enzyme, aldehyde dehydrogenase (ALDH).

Normally, acetaldehyde is quickly converted to acetate and excreted from your body. But when you have had a lot of alcohol to drink, your liver may not convert the acetaldehyde as quickly as usual, and it may build up enough to contribute to the nausea, vomiting and sweating of a hangover.

Direct effects of alcohol

alcohol effects

1. Headache

Alcohol dilates the blood vessels in your brain, which can trigger a headache — one of the most common symptoms of a hangover. Dehydration also contributes to the throbbing type of headache that many people associate with hangovers.

2. Sleep

While many people find that they fall asleep more easily after drinking alcohol, they often report sleeping less soundly. This is because your body is rebounding from the depressive effect of alcohol, disturbing your normal sleep rhythm, so you won’t get as much deep sleep.

3. Low blood sugar

Alcohol can prevent your body from maintaining its usual tight control on blood sugar levels, causing a low blood sugar concentration. Low blood sugar is one of the main causes of fatigue and weakness that people experience as part of a hangover.

4. Dehydration

Alcohol is a diuretic, meaning that it stimulates your body to increase urine production, depleting your body of fluid. This can cause dehydration if you have consumed a lot of alcohol. Symptoms of dehydration may include dry mouth, thirst, dizziness and headache.

5. Gastrointestinal effects

Alcohol can cause inflammation of your stomach lining (gastritis), leading to nausea, vomiting and stomach pain. Alcohol also stimulates your stomach to produce excess acid, further contributing to nausea and vomiting. In severe cases this can cause even more inflammation and there can be blood in the vomit. If this happens you should see your doctor. Some people also have diarrhoea because alcohol causes your small bowel to absorb less water and propel its contents along more quickly.

Alcohol withdrawal

Some experts believe that at least some of the symptoms of a hangover, such as sweating, anxiety, tremors and increased heart rate, are due to the effects of withdrawing from alcohol. Your nervous system may need to re-adjust as your blood alcohol level returns to zero.

How to avoid a hangover

It’s no secret that the more alcohol you drink, the more likely it is that you’ll have a hangover. So limiting yourself to the recommended number of standard drinks is the best way of avoiding a hangover. Other tips to decrease your risk of a hangover include:

  • avoid drinking quickly;
  • minimise drinking carbonated drinks, such as champagne, which tend to raise your blood alcohol level more quickly than other drinks;
  • avoid drinking on an empty stomach; and
  • not smoking when you drink.

Another factor contributing to hangovers are compounds found in most alcoholic drinks known as congeners. Drinks with a higher concentration of these substances tend to cause more severe hangovers. So steer clear of bourbon, whiskey, brandy and red wine, which all contain high concentrations of congeners. Gin and vodka tend to contain fewer congeners than other alcoholic drinks.

Last Reviewed: 2 September 2009


1. Mayo Foundation for Medical Education and Research [website]. Hangovers (updated Dec 2007). Available from: http://www.mayoclinic.com/health/hangovers/DS00649 (accessed Nov 2009)


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