Why you got that hangover

When alcohol is absorbed into the bloodstream and reaches the brain, it produces the pleasant sensations which are the whole point of having a social drink," says Dr Virginia Warren, a public health doctor who is associate medical director of Bupa.

"The trouble arises because the body can only process one unit of alcohol per hour. One unit means a single measure of gin, or a small glass of wine - not the generous glassfuls we are used to - or a half pint of beer. That one-unit-per-hour is the capacity of the liver and kidneys to get rid of alcohol.

The other substances which alcoholic drinks contain-apart from alcohol, are known as congeners, which are effectively poisons, which your liver will try to render into harmless substances. Congeners are what makes one red wine subtly different from another; they are another form of alcohol. Drinks which are darker coloured and have more flavour - such as red wine or brandy - have more congeners (alcohol is, after all, a colourless liquid).

"These poisons stack up in the body awaiting elimination. As their levels rise, they interfere increasingly with the biochemical processes of the body. The main effect is to dehydrate you, which makes you feel rough. Secondly, as your metabolism switches over to deal with the alcohol and congeners, it detracts from its ability to keep your blood sugar levels stable, so these fall, making you feel worse.

"If you eat salty snacks, it only exacerbates the dehydrating effect by giving your kidneys an extra salt load to deal with, when they are trying to cope with the dehydration. It is dehydration which brings on the familiar headache of a hangover, made worse by low blood sugar, and the lack of sleep which is often involved after a marathon drinking session doesn't help.

"What you need is time to allow your liver to do its job, enough non-alcoholic fluid to help the kidneys remove waste products, and perhaps something sweet to give a short-term lift to blood sugar levels until these stabilise."