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 New Zealand?
Acknowledging the fact that driving under the influence of weed can cause serious psychomotor impairments and lead to unwanted road accidents, the government of New Zealand is currently working on addressing this issue.
New Zealand’s Minister of Transport, Julie Anne Genter, introduced the Land Transport (Drug Driving) Amendment Bill into Parliament on 30 July 2020. This Bill proposes roadside testing of oral fluid (saliva) as a way to identify the presence of drugs in the driver’s body.
If the Bill gets adopted, police officers would have the right to stop any driver at random and administer the drug test. The test will test for the presence of cannabis, opiates, cocaine, ecstasy, benzodiazepines, methamphetamine, etc. in the driver’s blood and deliver the results in 2-5 minutes.
Ms. Genter is aware that these tests might not be foolproof, so in addition to the roadside tests, the people tested positive will undergo a second test in the laboratory before they receive a fine and immediate suspension from driving for at least 12 hours.
This information was published by Ms. Genter herself in a blog post on the official website of the Green Party of Aotearoa, where she added that “oral fluid tests will check for some impairing prescription drugs. However, a medical defense will be available in instances where people have taken medication in accordance with their prescriptions”.
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.
New Zealand is working on introducing a bill to Parliament in order to regulate random roadside saliva testing, so if you decide on driving, you should wait 24 hours for your body to detox completely. Currently driving while intoxicated is considered punishable by law so it would be in your best interest to wait this period out before getting behind the wheel.
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