How marijuana affects your ability to drive

Laws governing marijuana usage have changed dramatically over the last decade. Once reserved exclusively for medical use, marijuana has now been legalized in 18 states, and data from the National Conference of State Legislatures indicates that medical use of cannabis products is now legal in 37 states, four territories, and the District of Columbia. A similar shift has taken place in Canada, where cannabis was legalized with restrictions in 2018.

The shifting dynamic surrounding marijuana has been welcomed by some people, but left others wondering what the unintended consequences of legalization could be. One such curiosity concerns driving under the influence of marijuana.

Recognition of the effects of alcohol on driving ability is an important way to ensure roads stay as safe as possible for motorists, cyclists, and pedestrians. Ignoring or downplaying these effects could lead to accident, injury, or even incarceration. Marijuana can impair driving ability, whether it’s used for medical purposes or recreation, and a medical marijuana exemption does not protect an individual from the legal consequences of driving while impaired.

According to the California Office of Traffic Safety (COTS), marijuana poses a potentially significant safety risk on the road. Data from the COTS indicates that 42 percent of all drivers who were tested after dying in motor vehicle crashes tested positive for legal and/or illegal drugs. Though not all of those drivers had used marijuana prior to being involved in fatal crashes, such data underscores how important it is for drivers to recognize how marijuana use, even in places where it has been legalized, can impair their ability to drive.

Marijuana and the brain
The COTS reports that marijuana affects the part of the brain that’s responsible for body movement, balance, and coordination. Drivers’ brains and bodies may be slower to react after ingesting marijuana, which can increase their risk for motor vehicle accidents. In addition, the COTS notes that researchers examining the effects of marijuana use on the brain have determined that marijuana negatively affects attentiveness and the perception of time and speed.

Marijuana and risk-taking
The COTS indicates that the more marijuana drivers ingest, the more risks they take while driving. That’s an important point to consider, as many individuals insist they drive more cautiously after ingesting marijuana than they normally would. But caution dwindles as drivers increase their marijuana intake, potentially compelling drivers to take more risks on the road.

Marijuana, driving, and timing
The COTS reports that the effects of marijuana are strongest within 30 minutes of consumption. In fact, drivers who drive immediately after consuming marijuana may increase their risk of being involved in a motor vehicle accident by as much as 35 percent.

Though millions of people are celebrating the legalization of marijuana, it’s still important for drivers to exercise and emphasize caution when consuming cannabis.