Incidences of marijuana and driving are common, with 12% of teenage drivers reporting driving within an hour of smoking marijuana. Marijuana is also the drug that teens combine most often with alcohol use. This is noteworthy because the combination of these substances can have unpredictable physical and psychological effects (like nausea or panic) and can lead to more risk taking

What has Research Found?

The risk of causing a vehicle accident significantly increased after marijuana use according to several meta analyses. Furthermore, there are studies linking cannabis use to the risk of accidents doubled. In two European studies, Marijuana is the illicit drug most frequently found in the blood of drivers who have been involved in accidents. ‘High’ drivers were about twice as likely to cause a fatal accident than drivers who had not used drugs or alcohol.

The role marijuana plays in accidents is unclear at times. It can remain in the body for days or weeks after intoxication and users are often using alcohol as well. Drivers with higher levels THC in their blood are three to seven times more likely to be responsible for an accident than drivers who had not used drugs or alcohol. Furthermore, the risk associated with marijuana in combination with alcohol appears to be greater than either drug by itself.

Research in Action

If your child has been using marijuana and driving, he or she is abusing the drug and may have a significant problem. An assessment can determine the seriousness of the problem. Most of all, even one event of driving high can be devastating. The changes in perceptions and reflexes make the young driver even more dangerous.

It may surprise you, but research has shown that cannabis is more risky than many other drugs of abuse because it stays in the brain of a regular user for weeks. In comparison, alcohol leaves the system more quickly.

National Institute on Drug Abuse, Does marijuana use affect driving? August 2016

DRUID Final Report: Work Performed, Main Results and Recommendations. EU DRUID Programme; 2012. http://www.roadsafetyobservatory.com/Evidence/Details/10940