Researchers from the School of Public Health, the School of Medicine, Boston Medical Center, and University of Victoria found that people who died in crashes involving cannabis had 50 percent greater odds of also having alcohol in their system.

For the study, which was funded by the National Institute on Alcohol Abuse and Alcoholism, researchers analyzed 19 years of data from the Fatality Analysis Reporting System, a national database of fatal crashes on public roads. The percent of crash deaths involving cannabis more than doubled from 9 percent in 2000 to 21.5 percent in 2018, and the percent of deaths involving cannabis and alcohol also more than doubled from 4.8 percent to 10.3 percent. Cannabis was a risk factor for alcohol co-involvement, even at levels below the legal limit.