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Last Updated: Tuesday, 9 December, 2003, 15:33 GMT
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How many units is my drink?
 EFFECT OF ALCOHOL ON THE BODY 1. Absorption of information restricted; memory impaired; inhibitions lowered 2. Tunnel vision; difficulty in distinguishing light intensity 3. Central nervous system impaired; intestinal irritation can lead to ulcers; high levels can lead to coma or death4. Change in fat metabolism, eventually leading to scarring of the liver5. Sexual performance inhibited, possibly leading to impotence6. Co-ordination and motor skills impaired; increased swayingSource: Johns Hopkins University
As the range and strength of alcoholic drinks continues to grow, BBC News Online looks at how to work out exactly how much you are drinking.

Many of us are familiar with the system of measuring alcohol content in "units".

We are told, for instance, that for women 14 units of alcohol a week is the recommended limit, and for men 21.

Many of us have been told a glass of wine is the equivalent of one unit, and a pint of lager two.

But the system was devised over 20 years ago, and since then the strength and variety of drinks available has changed dramatically.

One glass of wine rarely now equals just one unit of alcohol.

This rough guide was based on a glass of wine at 8% ABV (alcohol by volume) in a 125ml glass - a measure and strength no longer widely available.

Nowadays, a standard glass of wine is served in a 175ml glass and is often up to 13% ABV, which adds up to 2.3 units.

Similarly, a half-pint glass of beer is only equivalent to one unit if the alcohol content is 3.5%, but most lagers on sale today are much stronger and a pint could easily be 2.8 units.

How many units?

But there is a sum which helps you work out how many units you have drunk.

You need to know the strength of the drink (%ABV) and amount of liquid in millimetres (one pint is 568ml; a standard glass of wine 175ml).

You multiply the amount of drink in millilitres by the percentage ABV, and then divide by 1,000.

For example, if you order a pint of strong lager at 8% ABV:

1 pint (568ml) X 8 = 4,544

Divided by 1,000 = 4.544, or 4.5 units

That is much stronger than the two units many people assume it would contain - and means just over three pints of strong lager would reach the recommended weekly limit for women.

What about drinking and driving - how many units is safe to drink before getting behind the wheel?

The legal drink-drive limit is 80mg per 100 millilitres of blood.

But this cannot easily be translated into alcohol units as it can be affected by build, sex, whether food has been eaten, and a host of other factors.

 ALCOHOL CONTENT Standard (175ml) glass of wine - 2 units Large (250ml) glass of wine - 3 units Pint of standard lager - 2.3 units Pint of premium lager - 2.8 units Pint of strong cider - 4.7 units
Campaigners say there is therefore no safe amount to drink before driving, because it is so difficult to tell what effect the alcohol will have on you.

Another important consideration is how long the each unit will stay in your system.

Only 10 minutes after having a drink, 50% of the alcohol will be in your bloodstream.

After an hour all the alcohol will have been absorbed.

On a typical night out you may easily have 200mg/100ml of alcohol in the blood by midnight, which will not be fully flushed out until the following afternoon.

And contrary to popular belief, it is impossible to speed up the processing of alcohol through your body any faster.

A cold shower or cup of coffee will not help - it just takes time.

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