Don’t forget: breath alcohol levels continue to rise after you stop drinking!

By Anna Sandiford 06/11/2013

I have just been watching Campbell Live where the presenters had a two-hour lunch with alcoholic drinks and then tested themselves with a breath alcohol screening device to see how they felt to drive compared with what alcohol they had actually consumed.  This is all as a result of the government’s (good, in my opinion) idea to lower the drink drive level from 80 mg alcohol/100 ml blood to 50 (which is from 400 microlitres of alcohol per litre of breath down to 250).  My main agreement with this is based on the level of impairment people experience at 80 compared with the generally lesser impairment they feel at 50.

There are three points that also need to be taken into account here (they may have been covered before but let’s go over them again):

1.  Drinking alcohol after eating slows down alcohol absorption.  This means that the resulting blood (and therefore breath) alcohol concentration will be lower than if the person had consumed the same alcohol on an empty stomach.  It is all well and good to say that a person had a meal when they were drinking – but if they drank any alcohol at all prior to eating (and assuming they hadn’t eaten in the few hours beforehand) then that alcohol consumed on an empty stomach will absorb quicker than the alcohol consumed after the meal is started.  Net result: the person will feel the effects of those pre-dinner drinks quicker than if they had waited until after they had started eating before they started drinking alcohol.  Aperitifs are not necessarily a good thing…

2.  As with many of these media demonstrations of alcohol consumption and breath testing, the Campbell Live demonstration showed people drinking and then testing themselves within minutes.  This is reasonably representative of what people do – they finish their drink and then may drive straight away.  The important thing to remember here is that it takes (on average) between 30 minutes and an hour (sometimes longer) for all alcohol consumed to be absorbed into the bloodstream.  What that means in real life is that a person’s blood and breath alcohol levels continue to rise in the time after they stopped drinking – which may be the time they are driving.  If they are soon stopped by the Police or involved in a road traffic incident then they may find their breath alcohol level is higher when they are stopped that it was when they were at the pub.

3.  A person often feels more drunk as their blood alcohol level is rising than they do when they are sobering up – you can have a blood alcohol concentration of 80 on the way to 120 and feel more drunk on the way up to 120 than when you are coming back down to 80 after having achieved 120.  This is referred to as the Mellanby Effect.


Overall, I think the reduction is good news for a country with a social alcohol drinking issue – but remember the above.  And, if in doubt, don’t drink and drive!