Fraser Horton
Fraser Horton
Last Updated on September 29, 2020

Cannabis users often make the fatal mistake of driving either right after they’ve smoked a joint or only a couple of hours after, thinking the effects must have faded already. 

In reality, this type of behavior isn’t tolerated around the world and is punishable by law, as you’re putting both your life and the lives of others at risk. Your driving ability can be compromised for a number of reasons, but the main ones are driving under the influence of alcohol and drugs.

Drunk driving is considered a felony when your blood alcohol content (BAC) is above the legal limits regulated by the state. If you are stopped, local law enforcement can do a field sobriety test, and you can be charged with a DUI.

Whereas driving under the influence of alcohol has an upper limit for how much you can drink before you get behind the wheel, if your THC blood levels are elevated and you are caught under the influence of weed when driving, there is typically zero tolerance. As marijuana becomes more available every day, some companies are even trying to develop a sort of breathalyzer to test for it. 

So taking all of this into account, is there definitive data on how long after smoking weed you can drive?

In this article, we’ll explain the effects that weed has on driving and provide the answer to the “should you drive after smoking weed” question, and share how long you should wait before getting behind the wheel.

How Does Using Recreational Marijuana Affect Your Driving Skills?

Multiple studies have found that marijuana use can cause serious impairments on driving-related tasks and lead to drug-impaired driving (Ogourtsova et al, 2018; Hartman et al, 2015; Battistella et al, 2013). The studies have shown that driving while stoned produces the following effects:

  • Temporary impact on reaction time and motor coordination in complex driving situations.
  • Changed perception of time and speed.
  • Temporary impairment of short-term memory and decision-making processes causing divided attention in complex and time-pressured situations.
  • Worsened overall driving performance when measured and assessed with driving simulation techniques (e.g. having trouble maintaining lateral road position within a single lane).

The negative effects of driving high depend on the dosage taken by the driver and the amount of THC in it, and whether or not the driver is a frequent smoker. Regular smokers have been found to have a higher tolerance to the above-mentioned impairment effects. 

Unlike alcohol, weed-induced driving impairment is not characterized by violent and aggressive behavior. However, combining weed with alcohol significantly increases the risk of road accidents and driving performance impairment.

Are There Studies That Show How Long After Smoking Pot You Can Drive?

To assess the amount of time that a person is considered an impaired driver after smoking pot, a Canadian study at the McGill University tested 45 young recreational weed users (21 male and 24 female participants) aged 18-24. 

Before the experiment, the participants inhaled a standard dose of 100 mg of the Cannabis drug containing 13% THC levels. One joint typically has between 150-300 mg.

Next, the driving-related performance of the participants was examined at the one-hour, three-hour, and five-hour mark. The results showed that 100 mg of marijuana had no effect on simple driving tasks but there was a significant impairment on complex and especially novel driving tasks even after five hours of being under the influence of marijuana.

Therefore, the study advises that smokers should wait at least six hours for the effects of marijuana to decrease before they get behind the wheel, although a 24-hour period is recommended for the body to purge from the drug completely.

How Long After Smoking Marijuana Can You Drive in Australia?

Driving under the influence of drugs or alcohol reduces your ability to foresee and understand the ramifications of your actions. Different countries around the world have different ways in which they try to tackle this problem. 

Australia is the only country in the world that has implemented a working roadside drug test program. Australian police officers have the right to stop drivers and administer Mobile Drug Testing (MDT).

The test was devised by the New South Wales Center for Road Safety. The NWS government has zero-tolerance for driving under the influence of any drug, weed included. MDT is able to identify the presence of cannabis, cocaine, ecstasy, and methamphetamine. 

The testing procedure requires drivers to “wipe an MDT test stick down your tongue” (NWS Road Safety) after which the results will show up within minutes. When testing for cannabis, MDT detects the presence of THC – weed’s main psychoactive compound – up to 12 hours after smoking weed.

Weed-influenced driving is a serious offense, so if the results come out positive and this is your first-time offense, they’ll be taken to a laboratory for confirmation. If the laboratory confirms the presence of cannabis in your blood, you’ll receive a fine and your driving license will be suspended for the following three months. Second-time offenders are taken to court and risk losing their license.

However, the test’s effectiveness has been criticized and called into question by a number of Australian legal experts, as there have been complaints that the test showed positive even if the driver was completely sober (e.g. smoked weed two weeks prior to the test). Others reported being punished for “rubbing hemp balm on their skin”.


Driving a motor vehicle comes with great responsibility and should never be taken lightly. You must be alert, mindful about your surroundings, completely in control of the vehicle, and ready to react to any unforeseen road situation. Whether you use medical marijuana or use marijuana recreationally, you should always prioritize driving safely.

Studies have shown that smoking cannabis before driving can seriously affect and temporarily decrease our psychomotor skills. As a result of that, we become a danger to ourselves and our environment which is why driving under the influence of cannabis is illegal and punishable by law around the world.

Although research suggests waiting around six hours after smoking weed, in Australia, the Mobile Drug Testing can identify weed in your blood up to 12 hours after smoking. Therefore, to be completely safe, as some studies have also suggested, avoid driving in the next 24-hour frame.

Additional Sources

Ogourtsova T, Kalaba M, Gelinas I, et al. (2018) Cannabis use and driving-related performance in young recreational users: a within-subject randomized clinical trial. CMAJ Open  E453–E462.

Hartman, R. L., Brown, T. L., Milavetz, G., Spurgin, A., Pierce, R. S., Gorelick, D. A., Gaffney, G., & Huestis, M. A. (2015). Cannabis effects on driving lateral control with and without alcohol. Drug and alcohol dependence, 154, 25–37.

Battistella, G., Fornari, E., Thomas, A., et al. (2013). Weed or wheel! FMRI, behavioural, and toxicological investigations of how cannabis smoking affects skills necessary for driving. PloS one, 8(1), e52545.


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