Note – Evidence and research around this topic continue to emerge and evolve. The post below is based on the best information currently available (Dec 2025).
TL;DR: It is NOT safe to drive after using cannabis. Cannabis can negatively affect your ability to drive safely, even hours after use.
While it’s tempting to think driving after using cannabis is much safer than alcohol, this really isn’t the case. Driving while high can slow your reaction time and disrupt coordination, perception, attention span, and decision-making. These effects can last for several hours after cannabis use, although the exact length of cannabis effects can vary based on product type, how it’s consumed, and the amount of THC. THC, or delta-9 tetrahydrocannabinol, is the main chemical that gets people high from cannabis.
One 2022 study found that drivers who smoked cannabis were poor drivers (e.g., veering out of their lane) on simulated roads up to 4.5 hours after usage. This was even after accounting for THC amounts and intensity of prior cannabis use. Concerningly, a majority of the study’s participants felt ready to drive 1.5 hours after smoking cannabis, despite their driving performance being no different than immediately after use.
Some people may try to compensate for cannabis effects (e.g., slowing down, being more “cautious”). Many people who regularly use cannabis don’t think their driving ability changes while high. One 2019 AAA survey found that an estimated 14.8 million drivers approved getting behind the wheel within 1 hour after marijuana use (7%), more than when impaired by prescription drugs (3%), drowsiness (1.7%), or alcohol (1.6%). While impairment may be less pronounced among regular cannabis users than in new or occasional users, *any* level of high can still negatively affect people’s ability to drive.
Research shows mixed results on whether cannabis use makes road accidents more likely, but many recent high-quality studies suggest an increased risk of crashes. Between 2011 to 2014, almost a fifth of fatally injured drivers sampled for drug usage in Canada tested positive for THC (although this isn’t a perfect measure for how high someone is—more on that later). Combining cannabis with even small amounts of alcohol can also greatly increase the risk of (potentially deadly) road accidents than with either cannabis or alcohol alone.
While state laws around driving under the influence of cannabis vary widely, it is generally illegal to do so in all 50 states. Some states, like Virginia, forbid passengers from using cannabis, even if they themselves aren’t driving. Penalties for driving high include fines, the loss of your license, and even jail time. Although many people don’t think they’ll be caught by the police after driving high, there are still ways for officers to detect possible cannabis usage behind the wheel (e.g., car/breath smell, dilated pupils, oral sampling), even if methods aren’t perfect. Researchers are working on creating new testing tools, like a portable breathalyzer, to help police better detect cannabis use in drivers. Scientists are also working on long-term research to better understand the effects of cannabis legalization and usage on driving.
⚖️ Policy Alert!
Driving under the influence (DUI) laws for cannabis are usually similar to those for alcohol, but they don’t account for some key differences between the two substances. Alcohol use is typically detected with a roadside breathalyzer or through Blood Alcohol Concentration (BAC) levels, both of which are highly accurate measures for how drunk someone is behind the wheel. However, cannabis levels are currently measured via THC, which can remain high for days, even a month, after usage. This means it’s difficult for officers to determine how recently a driver used cannabis or how high they are, even with blood or saliva testing. There’s also no nationally standardized THC blood concentration to determine whether someone is high behind the wheel, unlike the established BAC of 0.08% for drunk driving.
🌿 How can I use cannabis safely?
While we work to better understand how cannabis affects our health, here are some tips if you do live in states with legalized cannabis use:
➡️ Make plans to stay at home after cannabis usage.
➡️ Find alternative transportation if you do need to get back on the road (e.g., a sober friend, rideshare, walking).
➡️ Get familiar with your state’s laws on cannabis usage behind the wheel. The science behind cannabis-impaired driving is still evolving, so current state laws might not adequately protect against unsafe levels of intoxicated driving (see Policy Alert above).
➡️ Let your healthcare providers know if you’re using recreational cannabis. Certain medications put you at greater risk of bad, even dangerous, reactions to cannabis.
✨ Bottom line: Just because you don’t feel high after using cannabis doesn’t mean it’s safe for you to drive.
Stay safe. Stay nerdy.
With love,
Those Nerdy Girls
Additional Resources:
National Conference of State Legislatures: Drugged Driving | Marijuana-Impaired Driving
