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Can mouthwash cause a ‘positive’ RBT? What about an ‘Up & Go’?

“As a P-plater I was surprised to hear there were a number of things that could cause a positive RBT result, even if I hadn’t been drinking. Can you explain why some mouthwashes may do this? Also, I’ve heard that drinking a vanilla ‘Up & Go’ can cause the same problem – is that true?

In Australia, all learner, P1/P2 provisional, probationary or restricted drivers must have a blood alcohol concentration (BAC) of 0.00. As you’ve said, unfortunately, when a young driver is breathalyzed as part of a random breath test (RBT) there are a number of things that could cause a positive reading (i.e., over 0.00) in the preliminary test even if you haven’t drunk alcohol.

Certainly, mouthwash seems to be one of the worst culprits here as some brands can contain quite high levels of alcohol. Many people who gargle do so just before they go out and if you’re pulled over by the police and breathalyzed shortly after leaving home there is a chance that you could get a positive reading due to ‘debris’ of alcohol in your mouth. You’re certainly not intoxicated and that’s why you can’t be charged based on the preliminary test – it’s the evidentiary test that counts. This test, conducted after you’ve failed the first, is carried out elsewhere – either in a ‘booze bus’ or a police station – and is more specialized and far more accurate. It’s also done some time later – usually about 15 mins after the first – and by that time any debris should have moved and won’t be picked up. Nowadays ‘alcohol-free’ mouthwashes are available and it’s recommended that all P-platers use these products if they can.

It’s important to note that full licence holders are far less likely to have this problem. 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 don’t 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’s possible to fail that preliminary test. There’s a simple 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 similar story got extensive media coverage across Australia a number of years before, this time it was a ‘Bubble ‘O’ Bill’ ice cream that caused a problem for a driver with the same device on his car. This man appeared in court and requested that his lock be 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’s important to note that both these cases involve interlock devices on cars and not a breathalyzer at an RBT. It’s likely that both men probably consumed the product and then blew into the device straight away. That’s not how an RBT is conducted. But why would these products possibly cause the problem even in those circumstances? Some believe it was likely 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 young drivers are rarely, if ever, told this can happen, there are some foods and liquids that can cause an elevated reading in the minutes after they are consumed, but that’s why there’s a break between the two tests administered at an RBT. 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 could possibly be there and prevent an unpleasant and unnecessary visit to the ‘booze bus’ or the local police station.

First published: July 2016
Reviewed and updated: March 2024

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