What are the causes of a hangover?

“If getting drunk was how people forgot they were mortal, then hangovers were how they remembered.” – Matt Haig, The Humans.
Hungover egg
It is often said that dehydration causes a hangover. But while it is true that dehydration is a major cause of a hangover, leaving you dry mouthed, dizzy, and with a crippling headache, the suffering does not stop there. As anyone who has gone overboard with the plonk will know, the dreaded hangover is often compounded by further unpleasant aftereffects including, but by no means limited to, nausea, fatigue, and often depression.

There are numerous factors that contribute to a hangover. These include: the direct effects of alcohol on the body, the symptoms of alcohol withdrawal, and the toxic effects of the metabolic (breakdown) products of alcohol. The characteristics of a hangover may also differ from person to person and usually depend on both the type and the amount of alcoholic drinks consumed.

The principal alcohol found in alcoholic beverages is called ethanol. It is a substance the body can tolerate relatively low levels of, but it is in fact poisonous; its regular consumption can have very detrimental effects.

Why the hangover?

Firstly, ethanol is a diuretic and drinking it leads to increased urination. It prevents the release of a hormone called vasopressin – a substance that tells the kidneys to conserve water when you haven’t drunk enough. Drinking alcoholic drinks therefore makes you visit the toilet more frequently and the urine you produce will be more dilute.

Secondly, ethanol acts as an irritant towards the stomach and intestines, causing your stomach to feel tender and sore the next day, and can also lead to vomiting or diarrhoea. These two factors result in fluid loss and electrolyte (salts) imbalance. Ethanol, along with other alcohols, also affects several hormones and messaging molecules in the brain that are implicated in the cause of headaches. In addition to this, alcohols induce liver damage and cause the accumulation of fat compounds in liver cells. Effects on the liver can also lead to hypoglycemia (low blood sugar), potentially contributing to the fatigue and shakiness often experienced during a hangover.

Unfortunately, the torture of a hangover is not just caused by the direct effects of ethanol alone. After ethanol has made its way into the bloodstream, it starts to be broken down. The first substance ethanol becomes as it is degraded is called acetaldehyde (produced by the enzyme alcohol dehydrogenase) which is a chemical that is significantly more toxic than ethanol. And as its levels increase after a drinking binge, it can cause further toxic effects, including severe headaches, sweating and vomiting. Another important point to consider is that these enzymes have other duties in the body, which are neglected as they deal with the sudden influx of alcohol. Such neglect of other important functions contributes further to low blood sugar levels and subsequent feelings of tiredness. Added to that, there are also numerous other chemicals, known as ‘congeners’, which are substances other than ethanol (such as methanol, and various aldehydes and esters) produced during fermentation, which contribute to the taste, smell and colour of alcoholic beverages. Many of these can have similar toxic effects on the body – and could explain why inferior quality wine is more likely to cause a hangover.

Finally, an often overlooked contributor to the hangover experience is the effect of alcohol withdrawal. For regular drinkers, withdrawal symptoms include shaking, agitation and anxiety (for heavy drinkers who stop suddenly, withdrawal can be life-threatening). Any withdrawal symptoms have the effect of intensifying a hangover as well as disrupting sleep, as the body struggles to adjust to the sudden stop in intake of alcohol, which is a sedative substance.

So to conclude, a hangover is often a smörgåsbord of unpleasant symptoms triggered by a variety of harmful substances found in alcoholic drinks. These act through many different processes (some of which are still being researched) and dehydration is by no means the only cause of your suffering. The NHS choices website has some advice on how to help ease the symptoms of a hangover. (The best bet is not to drink too much in the first place! Ed)

Answer by Phillip Lowe

Photo credit: Breakfast hangover 2 by 4ELEVEN Images, on Flickr


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Article by Phillip Lowe

December 18, 2014

Phillip has a Masters in Chemistry and is currently in the final throes of his PhD in Biological Chemistry at the University of Manchester, UK. Aside from science, his passions include football, rugby and the home brewing of ale and cider (which is drunk in moderation, naturally).


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