Can using mouthwash cause a 'positive' RBT? What about an 'Up & Go'?

My name is Joel and you talked to my Year 12 class recently. As a P-plater I was very surprised that there were a number of things that could give me a positive alcohol reading, even if I hadn't been drinking. Can you explain why some mouthwashes will do this so I can tell my friends who weren't at your talk? Also, I have a number of friends who believe that drinking a vanilla 'Up & Go' can cause the same problem - is that true?

Thanks Joel - as a P-plater you really do need to be extremely careful when it comes to alcohol. As I'm sure you know, all learner, P1/P2 provisional, probationary or restricted drivers must have a blood alcohol concentration (BAC) of 0.00.

Unfortunately, when a P-plater is asked by a police officer to take a breathalyzer as part of a random breath test (RBT) there are a number of things that could cause you to get a positive reading (i.e., over 0.00) in the preliminary test even if you haven't drunk alcohol. Certainly mouthwash seems to be the worst culprit here as some brands can contain quite high levels of alcohol. Nowadays you can buy 'alcohol-free' mouthwash and I certainly recommend all P-platers use this whenever they can. The problem is that most people who use mouthwash do so just before they go out and if you get pulled over by the police in the minutes after leaving your home and breathalyzed there is a chance that you could get a positive reading due to 'debris' of alcohol in your mouth. You are certainly not intoxicated and that is why you can't be charged based on the preliminary test - it is the evidentiary test that counts. This test, conducted after you have failed the first, is carried out elsewhere - either in a 'booze bus' or a police station - and is more specialised and far more accurate. It is also done some time later - usually about 15 mins after - and by that time any debris should have moved and won't be picked up.

It's important to note that full licence holders are far less likely to be affected in this way. Why? They don't have to be at 0.00! If a small amount of alcohol is detected (possibly caused by debris in the mouth) they do not fail that first test.

Other things can cause a similar problem with the preliminary test for P-platers - e.g., foods containing alcohol, whether it be a cake like tiramasu, a chocolate liqueur or even a dessert like a sherry trifle. Get a small amount of the sherry-soaked sponge stuck between your teeth and it is possible to fail that preliminary test! There is a way of avoiding this problem - all P-platers should carry a bottle of water in their car and before they set off take a swig of water and rinse your mouth out, removing any possible alcohol debris - so simple, yet so effective!

Now about the 'Up & Go'! I can't believe how many young people have heard about this - it makes little sense and it has taken me quite a while to work out where this actually came from… from what I can gather (and I can't guarantee that this is absolutely true) it all seems to have come from a Channel 7 News item that ran in December 2010. Apparently a man who had a breathalyser interlock on his car drank a vanilla 'Up & Go' and got a positive reading for alcohol and was subsequently unable to drive. He went to the media with the story and the story has rolled on ever since… Another story got extensive media coverage in Australia a number of years before about a 'Bubble 'O' Bill' ice cream that caused a similar problem for a driver with the same device on his car. This man appeared in court and wanted his lock removed because of the false reading caused by the ice cream. The magistrate found his claim difficult to believe and got him to purchase and eat the product in court. A breath test was then carried out and he blew a reading of 0.018!

It is important to look at these two cases and note that they both involve interlock devices on cars and it is likely that both men most probably consumed the product and then blew into the device straight away. That is not how an RBT is conducted. So why then would these products cause the problem? Some people believe it could be due to the presence of vanilla essence that can contain high alcohol levels but this is certainly not the norm and shouldn't be a concern for young drivers.

Although no-one usually tells P-platers that this can happen, there are some foods and liquids that can cause an elevated reading in the minutes after they are consumed, but that is why there is a break between the preliminary and evidentiary tests. As I've said, the best way for a P-plater to avoid an embarrassing moment is to always to rinse out their mouth before getting behind the wheel of a car - do this and that'll most likely remove any debris that may be there and prevent an unpleasant and unnecessary visit to the 'booze bus' or the local police station.

First published: July 2016