Marijuana and driving

Originally Published: February 18, 2000 - Last Updated / Reviewed On: December 1, 2014
Share this

Dear Alice,

I was wondering if you had anything about marijuana and driving.

Thanks. J

Dear J.,

Just about everyone has heard, "Don't Drink and Drive" and "Friends Don't Let Friends Drive Drunk." But not as many realize that there are many dangers associated with getting behind the wheel of a car (or bus, train, scooter, bike, or plane) while high on marijuana.

Pot use impairs one's ability to reason and make decisions, and slows reaction time. In addition, motor skills and visual tracking ability are diminished. It has also been shown to negatively affect a driver’s ability to be attentive and their perception of time and speed.  Driving while high is also not safe because users usually feel a bit tired and have difficulty concentrating after using. Sometimes people experience anxiety and/or visual, perception, and time distortions, none of which would help with navigating a vehicle on a road, or even in the driveway. Also, marijuana impairs memory formation, so if someone is given directions of where to drive while high, there's a chance that s/he won't quite remember how to get from point A to point B once the trip has begun.

Now, you might be asking yourself, “Self, what if I live in a state that has legalized marijuana?”  For instance, in Colorado, if you are high behind the wheel you can still get arrested for a DUI (driving while under the influence violation). Like alcohol, Colorado has put into place an impairment level — specifically if you have five or more nanograms of active tetrahydrocannabinal (THC), the main psychoactive chemical in marijuana, per milliliter of blood, you are impaired. Different states may have different laws, so you may want to check out the laws in your own state regarding marijuana and driving.

Keep in mind that many other drugs — whether they be legal or not, recreational or prescription — affect cognition and motor skills. In fact, 18 percent of deaths caused by motor vehicle accidents are due to drug use (which does not include alcohol). Also, research has shown that combining marijuana with alcohol can have an even greater impact on someone’s ability to drive safely. To ride the road to safety, you should avoid operating heavy machinery (cars, trucks, tractors, amusement park rides, etc.) until you've checked into the effects of a drug you're taking on your ability to think straight and move smoothly. Also, if your health care provider has you start a new medication, you may want to discuss if it may affect your ability to drive safely.

For more information on marijuana, check out the Marijuana, Hash, & Other Cannabis section in the Go Ask Alice! archives.

Alice