Fraser Horton
Fraser Horton
Last Updated on October 5, 2021

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, where do things stand with smoking and driving? 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” and “can you drive high” questions, 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 the US?

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. 

Even if marijuana is legal in your country it’s never legal to drive while you’re high. If the police stop you and you test positive, you’ll be cited for driving under the influence. 

No matter what the legalization policy is, laws when testing positive to weed can vary between countries, and in the case of the US, between states. For example, in Colorado, any driver who tests above 5 nanograms of THC per milliliter of blood is considered “intoxicated”, and you can get fined if you are stopped.

Meanwhile in California, where marijuana is legalized, the rules are similar to the rules for alcohol. You can’t be high when driving and you can’t have an open container nearby. Since the legalization, there are problems with defining when the person is subject to marijuana impairment. Standard drug tests can sometimes show positive results even after the mind-altering effect of the marijuana wears off.

Generally, roadside drug testing in the US is done with oral tests, and further blood testing can be done in a lab. If you’re not a regular user, your body will probably detox from the presence of THC within 24 hours. This depends on your metabolic rate and how much you have consumed, among other factors. It is always better to wait out the high and be on the safe side when driving.

Conclusion

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.

Since laws in the US vary from state to state, your best bet would be to wait about 24 hours for your body to detox, and for the mind-altering effects to wear off completely. After that period you will be all good to go, and you can get behind the wheel without worries.

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. https://doi.org/10.9778/cmajo.20180164

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. https://doi.org/10.1016/j.drugalcdep.2015.06.015

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. https://doi.org/10.1371/journal.pone.0052545

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