Studies have found that, after alcohol, marijuana is the most frequently detected substance in the general driving population, as well as drivers involved in crashes. Fourteen U.S. states conducted toxicological testing between 2005 and 2009 on over 80 percent of drivers who died within one hour after a crash; alcohol was detected in 40 percent of the drivers, followed by cannabinoids in 10.5 percent of the drivers.

On August 21, 2014, a New York teenager was sentenced to prison after admitting he was high on marijuana when he smashed his car into a tree, killing four of his friends. Investigators determined that the teen driver had been driving over 100 mph prior to crashing and killing the four passengers. A blood sample obtained after the crash revealed that he had tetrahydrocannabinol (THC)—the chemical responsible for most of marijuana’s psychological effects—in his system.

In July 2013, a 21-year-old Michigan man was convicted of driving under the influence of marijuana and causing the death of his girlfriend after crashing his vehicle. A police report showed that the man had 2 ng/mL of THC in his blood six hours after the crash.