A study by McLean Hospital’s Mary Kathryn Dahlgren, PhD, Staci Gruber, PhD, and their team from McLean’s Cognitive and Clinical Neuroimaging Core and the Marijuana Investigations for Neuroscientific Discovery (MIND) program, has found that recreational cannabis use affects driving ability even when users are not intoxicated by marijuana.
Published in the Drug and Alcohol Dependence journal, the study “Recreational Cannabis Use Impairs Driving Performance in the Absence of Acute Intoxication,” finds that in addition to chronic, heavy, recreational cannabis use being associated with poorer driving performance in non-intoxicated individuals compared to non-users, the researchers linked earlier onset of marijuana use (under age 16) to worse performance.
Study at a Glance
- McLean researchers have discovered that recreational marijuana use affects driving ability even when users are not intoxicated
- The study, conducted through driving simulation, concluded that chronic, heavy, recreational marijuana use was associated with worse driving performance in non-intoxicated drivers compared to non-using healthy control participants
- Cannabis users had more accidents, drove at higher speeds, and drove through more red lights than non-users
- Earlier onset of marijuana use (regular use prior to age 16) was associated with poorer driving performance
- Findings may be reflective of increased impulsivity in those who initiate substance use during adolescence; further research will explore this association
Recreational cannabis use has expanded across the United States in the last several decades and so has public concern about the substance’s impact on activities that present safety issues.
While several studies have examined the direct effect of cannabis intoxication on driving, no other studies until now have examined the effects on driving in heavy marijuana users who are not high.
Gruber, who is among the world’s foremost experts in the cognitive effects of marijuana, said the idea that differences can be detected in sober cannabis users may be surprising to the public.
“People who use cannabis don’t necessarily assume that they may drive differently, even when they’re not high,” she said. “We’re not suggesting that everyone who uses cannabis will demonstrate impaired driving, but it’s interesting that in a sample of non-intoxicated participants, there are still differences in those who use cannabis relative to those who don’t.”
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