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If you’ve ever asked the question ‘how much can I drink before I drive?’ you may be surprised that the only correct response is: ‘that depends’. Although the law permits a “safe limit” of 80mg of alcohol per 100ml of blood (or 35mg per 100ml of breath), there is no definitive answer to how many drinks will ensure you stay within this limit.

This is because alcohol is one of the few substances that is volatile enough to enter the bloodstream without getting broken down by the body. When it enters the blood as alcohol – a drug and a depressant – it is circulated around to your brain.

The alcohol then slows the brain processes down, depressing its ability to make realistic self-criticism – so you think you’ll be fine to drive when in reality you won’t at all. The more alcohol circulating in the blood, the more the brain is affected.

The body’s ability to absorb and eliminate alcohol depends on many factors, including:

  • Strength of alcohol: it is absorbed quickest when the concentration of alcohol is 20-30%. So a glass of sherry (with an alcohol concentration of about 20%) increases the levels of alcohol in blood more rapidly than beer (at 3-8%), while spirits (at around 40%) delay gastric emptying and inhibit absorption. Aerated drinks get into the system quicker than non-fizzy ones;
  • Stomach contents: an empty stomach allows alcohol to pass quickly into the lower intestine (which does most of the work of absorbing alcohol). A full stomach delays this process – fatty foods are best and can even absorb some alcohol;
  • Body weight: this plays a role because water makes up 66% of the body. Therefore, a larger-built person will in effect be able to dilute alcohol better than a smaller-built one;
  • Body fat: this can also affect the 66% ratio, thus reducing the amount of alcohol that is diluted;
  • Gender: women generally have a slightly higher fat ratio compared to men, so tend to dilute less alcohol.

All of the above is also relative to the amount of alcohol drunk and the rate at which someone drinks it.

Elimination of alcohol from the body also varies slightly from person to person but, on average, the body eliminates one unit of alcohol every hour (1 unit = small glass wine; ½ pint weak beer). So, if you drink a bottle of wine (roughly eight glasses) into the early hours of 2012, it will take at least eight hours to get out of your system. This explains why many people are arrested for drink-driving the following morning. As there are so many factors to take into consideration when determining how much alcohol is too much for driving, the safest option will always to be to not take the risk and avoid drinking altogether.

If you do take risks and end up over the limit, then the consequences can shatter many lives. When I was a young policeman working in Monmouth, I recall going to an accident at breakfast time on Christmas morning in 1985. A father was taking his two young children to meet their mother, the car full of presents. It met a Mini coming the other way, whose driver lost control on a blind bend. They collided head on.

The father was dead when the police arrived on the scene and was being cradled by one of his children. The other child was badly injured. The young driver of the Mini was fine. He had been drinking the day before at the office party and was amazed to be still over the limit.

For more information, contact our Personal Injury and Accident Claims team.