“You recently spoke at my school and I’ve forgotten a piece of information that you gave us around alcohol and driving. How long does it take until a female can drive after going out the night before if she is on her P-plates?”
Without a doubt being aware of how long you have to wait before driving after drinking alcohol is incredibly important for P-plate drivers. Even full licence holders get this wrong and end up with a criminal record for drink driving and they’re permitted to have a blood alcohol concentration (BAC) of 0.05. P-platers need to have a BAC of 0.00! This makes it far more difficult for them to stay under the limit should they choose to drink alcohol.
In addition, females have to even be more careful in this area as they can take far longer to process alcohol (particularly P-platers under the age of 21 years, as their livers do not fully develop until this time). As a result, they need to wait much longer than their male counterparts before getting behind the wheel of a car.
When I present to Year 12s I use an actual case study of a young woman who has gone out and had a ‘big night’ (she drinks 9 standard drinks over a 4-hour period, registering a BAC reading of 0.24). She goes to bed at 2.00am and doesn’t return to 0.00 until 16 hours later! Realistically that means that she wouldn’t be able to drive the entire next day.
Unfortunately, too many people still follow a ‘guide’ that was provided to drivers when random breath testing (RBT) was first introduced in Australia, i.e., males can have 2 drinks in the first hour and then one drink every hour after that, and for females, one drink in the first hour, etc. Too many people see this as a ‘rule’, which it isn’t – it’s a guide, and a very rough one at that. It’s based on evidence that suggests the liver gets rid of around one standard drink every hour. It’s also assuming that we’re dealing with an adult male with a fully-developed, healthy liver. This very rough guide certainly doesn’t apply to the majority of P-platers.
My advice to young drivers is to never look at drinking in terms of simply the number of drinks consumed and certainly don’t try to do a mathematical equation to work out when you are able to drive. It can easily confuse you or lull you into a false sense of security when in reality there’s no ‘special formula’ you can use to calculate how long you should wait. As said, it can give you a rough guide but that’s about it … Therefore, it’s much better to think of it as the type of night you’re having and how you feel at the end of the evening (i.e., a ‘big night’) …
As such, my advice for a female P-plater (who must have a BAC of 0.00) who’s had a ‘big night out’ (whatever that may be for the individual) is to wait 24 hours from when she goes to bed (basically don’t drive the next day) to be absolutely sure that she is under the legal limit. The case study above shows that it took the 19-year-old woman 16 hours to get back to 0.00. It’s better to be safe than sorry so I tell young women to wait even longer (just to be sure) as they can have additional issues when it comes to processing alcohol, including their menstrual cycle and whether they are using medications that contain estrogen, such as birth control pills (which can slow down the processing of alcohol). There’ll certainly be some young women who will process alcohol far faster and get back to 0.00 relatively quickly, but as I always say, it’s better to err on the side of caution …
If you’re having just one or two standard drinks, not bottles or cans (which may be far more actual standard drinks), my advice for a young woman is to wait at least 12 hours from going to bed after drinking (once again, just to be absolutely sure!). Driving to a part-time job or to a sporting match the morning after having just a couple of drinks could get you into trouble.
By the time young men are around 19-years-old they should have a fully developed liver and be able to process alcohol fairly quickly. So, my guide for them is if they’ve had a ‘big night out’, they should go to bed and wait at least 12 hours from when they go to sleep. My strong suggestion is that even if they’ve only had one or two drinks the night before it’s always best to be safe and still wait for 12 hours from when they go to bed before driving the next day. Once again, some will process alcohol far faster than that and be back at 0.00 very quickly, possibly getting rid of alcohol at a rate of around one drink per hour, but be smart and wait, just in case.
It’s important to note though, that if a young male P-plater has made themselves sick or feel unwell in some way due to their drinking (i.e., they’ve had a ‘huge night’), they will need to wait much longer. To be absolutely certain that you won’t get booked for drink driving and find yourself in court facing a magistrate, I would recommend that young men avoid driving the next day. It’s just not worth the risk!
Please note that the advice provided is for information purposes only. As such, it cannot substitute for the advice of a legal professional.
First published: July 2016
Updated: November 2023