It’s starting to feel a lot like Christmas. But how much, if any, mulled wine can you drink at a party if you’re planning to drive home? Half of people are unable to gauge when they are too drunk to drive legally, according to new research from the University of Cambridge. If you’re driving back from any celebrations this Christmas, here’s what you need to know before deciding whether to have that festive tipple.
Drink-drive limits
David Davies, the executive director at the Parliamentary Advisory Council for Transport Safety (PACTS) and Julia Sinclair, a professor of addiction psychiatry at the University of Southampton, say that fundamentally you shouldn’t drink and drive.
In England, Wales and Northern Ireland the drink-driving alcohol limit for drivers is 80mg of alcohol per 100ml of blood (the “blood limit”) and 35mcg per 100ml of breath (the “breath limit”).
“England and Wales have a high drink-drive limit. But the Department for Transport advice generally has been: do not drink and drive because frankly you can’t tell when you’re over the limit,” Davies says. “People should be very wary about going online and trying to calculate how much they can drink. Wines have got stronger, so 14.5 or 15 per cent is not unusual. And glasses have generally got bigger.”
Consumer breath testers
“The main thing to clarify is that breathalysers — if good quality and calibrated correctly — will accurately and reasonably objectively measure the level [mg/100ml] of alcohol in the bloodstream, but that level will subjectively feel very different to different people. Specifically people who rarely drink will feel really quite intoxicated at levels under 80mg/100ml,” Sinclair says.
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“People who are ‘regular’ drinkers will not necessarily feel affected and so are more likely to drive thinking they are OK. They have become tolerant to alcohol. The neural pathways in the brain adapt to regular amounts of alcohol and so the brain down-regulates its own GABA [gamma-aminobutyric] system in anticipation, so that for the same amount of alcohol in the body you feel less intoxicated. As people drink, their judgment becomes impaired and they convince themselves that they are safer to drive, or feel they are willing to take the risk.”
When buying a breath tester, opt for high-quality brands such as AlcoSense. And always look out for the CE mark to show that the product complies with European standards. EN 16280 is a good benchmark for consumer devices.
“The only trouble with these Breathalysers is they can encourage people to drink up to the limit. They’re really designed to be used the morning after drinking, not while drinking,” Davies says.
Factors to consider
Size, sex and whether you’ve eaten before drinking can affect how alcohol is metabolised. Women produce smaller quantities of the enzyme alcohol dehydrogenase (ADH) than men, which is released in the liver and breaks down alcohol in the body.
Drink and drugs
“If people are on other ‘psychotropic medication’ such as painkillers or pregabalin this will interact and have an impact on how they subjectively feel, but not what is measured on a Breathalyser,” Sinclair says. “People are likely to feel more impaired on those other drugs in combination with alcohol, unless they are also tolerant to them due to long-term use.”
A couple of pints?
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“You can be beneath the limit but unfit to drive,” Davies says. People can have a couple of pints and may be under the limit. But you’ve got to be careful. What is the pint these days? Lagers and craft beers can be 7, 8 or 9 per cent.”
