Senior author Dr. Guohua Li of Columbia University's Mailman School of Public Health said the meta-analysis provides compelling evidence for an association between marijuana use and crash risk.
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," Li said in a statement.
"Given the ongoing epidemic of drug-impaired driving and the increased permissibility and accessibility of marijuana for medical use in the United States it is urgent that we better understand the role of marijuana in causing car accidents."
The study, published online in Epidemiologic Reviews, found evidence that crash risk increases with the concentration of marijuana-produced compounds in the urine and the frequency of self-reported marijuana use.
Of the nine epidemiologic studies analyzed, 8-of-9 studies found drivers who use marijuana are significantly more likely to be involved in crashes than drivers who do not.