Drivers who test positive for marijuana or report driving within three hours of marijuana use are more than twice as likely as other drivers to be involved in motor vehicle crashes. This is the conclusion reached by researchers at Columbia University who conducted a meta-analysis on the subject.
They also found evidence that crash risk increases with the concentration of marijuana-produced compounds in the urine and the frequency of self-reported marijuana use.
The analysis indicates that 28 percent of fatally injured drivers and more than 11 percent of the general driver population tested positive for non-alcohol drugs, with marijuana being the most commonly detected substance.
Guohua Li, MD, DrPh, professor of Epidemiology at Columbia University's Mailman School of Public Health, and his colleagues said that although this analysis provides compelling evidence for an association between marijuana use and crash risk, one should be cautious in inferring causality from these epidemiologic data alone.
However, "if the crash risk associated with marijuana is confirmed by further research, this is likely to have major implications for driving safety and public policy. It also would play a critical role in informing policy on the use of medical marijuana," they added.
The findings are published online in Epidemiologic Reviews.