What the research shows about marijuana and driving

"Several meta-analyses of multiple studies found that the risk of being involved in a crash significantly increased after marijuana use13 -- in a few cases, the risk doubled or more than doubled.14-16 However, a large case-control study conducted by the National Highway Traffic Safety Administration found no significant increased crash risk attributable to cannabis after controlling for drivers’ age, gender, race, and presence of alcohol.17"

Source: 

"Marijuana," National Institute on Drug Abuse, January 2017, last accessed March 5, 2017, p. 13.
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https://www.drugabuse.gov...

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