Drivers are being urged to be cautious about getting behind the wheel the morning after a night out over the Christmas period.
Alcohol stays in the blood much longer than you think - with factors such as height, size and weight affecting how long it takes your body to metabolise.
While some believe that they are alright to drive because they have been to sleep, they could in fact wake up still over the limit.
Denis McCauley, chairman of the Irish Medical Organisation’s GP committee, also warned partygoers that "lining your stomach" before having drinks could actually delay alcohol absorption.
He told the Sunday Times : "Y ou metabolise all alcohol at a very steady-state rate. If you have one pint, it will metabolise at the same rate.
"If you have three pints, it will metabolise at the same rate. So it actually comes out of your system at a slow enough rate."
Generally speaking, drinking two pints of regular-strength lager around 2.3 units each will put you comfortably over the limit, as would two ciders or two 125ml glasses of wine, although this varies from person-to-person.
Mr McCauley added: "If I had a cheese sandwich before I went out for a drink, I would metabolise even slower, because it would take longer for me to absorb that alcohol into my system, so it actually delays the alcohol absorption."
The legal limit for driving in England, Wales and Northern Ireland is 80 milligrams of alcohol per 100 millilitres of blood.
This limit was imposed in 1966 when the Road Safety Bill was introduced. In 1967 the breathalyser was introduced as a way of testing a person's blood alcohol level.
In Scotland the limit was reduced in 2014 to 50mg of alcohol in every 100 millilitres of blood.
But on average, the body "eliminates alcohol at the rate of one unit an hour,” according to Richard Allsop, emeritus professor at University College London.
He previously said: “So anyone who wants to calculate when they’ll be completely free of alcohol needs to find out how many units each of the drinks they usually consume contains and keep a tally for each session."
Each 250ml (large) glass of wine of 12% alcohol strength equates to three units. Six glasses at the office party — and you’ve consumed 18 units.
If you have your last drink at 11.30pm, it could be 6.30pm the following evening before all the alcohol in your blood has been eliminated.
At 9.30am, you could still have nine units in your blood, putting you well over the legal limit. And if your liver is damaged by regular heavy drinking, it will take longer to get rid of alcohol.
There's also nothing you can do to speed up the rate at which alcohol leaves your system.
Steve Horton, director of communications at Road Safety GB, previously said: "Black coffee or a cold shower will not sober you up.
“Coffee just means you’re awake and drunk, and a cold shower that you’re cold, wet and drunk."
