Over 10 million people age 12 or older are estimated to have driven under the influence of illicit drugs in the prior year, according to a 2009 National Survey on Drug Use and Health.
While marijuana is the most commonly detected non-alcohol drug in drivers, its role in causing crashes has been uncertain. Columbia Epidemiologists, led by Guohua Li, MD, DrPh, set out to clarify the matter.
The researchers performed a meta-analysis of nine epidemiologic studies and found that drivers who test positive for marijuana or who report using marijuana are more than twice as likely as other drivers to be involved in motor vehicle crashes. The researchers 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.
According to the researchers 8 of 9 studies found that drivers who use marijuana are significantly more likely to be involved in crashes than drivers who do not. The full study findings are published online in Epidemiologic Reviews.
The analysis also indicates that 28% of driver fatalities and more than 11% of the general driver population tested positive for non-alcohol drugs, with marijuana being the most commonly detected substance.
“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. Given the ongoing epidemic of drug-impaired driving and the increased permissibility and accessibility of marijuana for medical use in the U.S., it is urgent that we better understand the role of marijuana in causing car accidents.” Dr. Li.