Marijuana may interfere with reaction times and coordination, among other things, experts say. The authors of the new study said it is critical to determine the excess crash risk related to marijuana in different doses, strengths, and administration methods, such as smoking versus vaporization.
None of the studies in this grouping looked directly at medical marijuana, which is now legal in 16 states plus the District of Columbia in the United States.
However, one expert cautioned against inferring too much from this study, which was not designed to capture cause and effect.
"We can't really say yet that marijuana increases the risk by two or three times," said Chuck Farmer, director of statistics at the Insurance Institute for Highway Safety in Arlington, Va. "Most of their studies pointed to a very strong bad effect of marijuana on driving, but there are other studies out there that actually go the other way."
But other experts expressed some alarm at the findings. "At [its] annual meeting in late September, the Governors Highway Safety Association strengthened its drugged driving policy," said Jonathan Adkins, a spokesperson for the association.
"We see this as a national priority and are seeking a range of actions to address the problem comprehensively," Adkins said.
The U.S. National Highway Safety Administration has statistics on drug-impaired driving.
SOURCES: Guohua Li, M.D., DrPh., professor, epidemiology, Columbia University Mailman School of Public Health, New York City; Chuck Farmer, Ph.D., director of statistics, Insurance Institut
All rights reserved