Marijuana Use and Driving

As more states pass laws to legalize marijuana, many are unsure of the safety of marijuana use and driving. No level of marijuana use is acceptable for young drivers, even in states where it is legal. It is illegal and unsafe for teens to drive high, just like it is illegal and unsafe to drink and drive. A DUI is given to anyone who is suspected of driving under the influence of drugs or alcohol and can negatively impact your teen’s future.

In 2018, 27% of all adolescent DUIs in Colorado involved marijuana, according to a research bulletin from the Highway Loss Data Institute. A police officer can stop anyone suspected of driving with marijuana in their system. A DUI citation can result in expulsion from school and loss of college scholarships and grants.

In 2017, 49% of drivers ages 14-18 who currently use marijuana engaged in driving after using marijuana, according to research published in JAMA Network Open. Another study, published in JAMA Pediatrics, found that when compared to young adults, teens have a higher risk of becoming addicted to marijuana within the first year of use.

While the legal age for using retail marijuana is 21 and for using medical marijuana is 18 in some states, it’s never okay to drive while impaired. Although the limited body of work exploring the impact of THC (tetrahydrocannabinol, the active ingredient in marijuana) on driving is mixed, generally accepted results report a two-fold risk of a motor vehicle crash among drivers with any THC in the bloodstream.

Detecting clinically significant levels of THC in the body can be complicated, however. Urine levels, which in many states are equated to blood levels (and are both illegal), can reflect past use and may not reliably detect people who are actually driving high. An accurate roadside test for drug levels in the body doesn’t yet exist.

How Marijuana Use Affects Driving

While laboratory studies of people with THC in their bloodstream do not support significant impairment on single tasks, such as memory, addition, or subtraction, there may be more significant impact on multitasking and handling unexpected events (which are critical components of safe driving):

  • Marijuana can slow reaction time and the ability to make decisions.
  • Marijuana can impair coordination, distort perception, and lead to memory loss and difficulty in problem-solving.
  • Marijuana use can have long-term effects for teens and young adults on brain development. Neurodevelopment continues until at least the early or mid-20s, and marijuana use impacts how connections are formed within the brain.

The risk of impaired driving associated with marijuana in combination with alcohol appears to be greater than that for either by itself. Some researchers suggest that resources are better directed toward reducing drinking and driving or reducing the mixing of alcohol and marijuana while driving.

Students Against Destructive Decisions (SADD) offers a Contract for Life that promises the teen, both as driver or passenger, will call home for a safe ride instead of getting into a car when the driver could be intoxicated, high, or tired, which is very dangerous. Families may want to consider using this contract to encourage use of a code word when needed.

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Local enforcement agencies in Colorado and Washington, states where recreational use of marijuana is legal, report marijuana impaired driving as somewhat or very common.

More Marijuana Use and Driving Facts and Statistics

  • Car crashes have increased by as much as 6% in CO, NV, OR, and WA as compared with neighboring states that have not legalized marijuana for recreational use.
  • In 2017, 49% of drivers ages 14-18 who currently use marijuana engaged in driving after using marijuana.
  • Marijuana, like alcohol, negatively affects a number of skills required for safe driving, including coordination, memory, and judgment.
  • In 2021, 16% of high school students nationwide reported using marijuana at least once during the last 30 days.
  • In a recent federal study conducted during the COVID-19 outbreak, half of drivers who were seriously or fatally injured in motor vehicle crashes tested positive for at least one active drug, including alcohol, cannabinoids (active THC), and opioids.