Washington D.C. [USA], Jan 15 : Cannabis consumption can make people bad at driving even when they are sober and the ones who start with the habit early on in their lives, fare even worse on driving parameters.
These findings were derived from a study by McLean Hospital's Mary Kathryn Dahlgren, Ph.D., Staci Gruber, Ph.D., and their team from other institutions which was recently published in the Drug and Alcohol Dependence journal. It revealed that in addition to chronic, heavy, recreational cannabis use being associated with poorer driving performance in non-intoxicated individuals, the earlier onset of marijuana use (under age 16) is linked to further worsened driving test scores.
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.
Senior author Gruber, along with Dahlgren, used a customized driving simulator to assess the potential impact of cannabis use on driving performance. At the time of the study, marijuana users had not used intoxicated for at least the past 12 hours.
Overall, heavy marijuana users demonstrated poorer driving performance as compared to non-users. For example, in the simulated driving exercise, marijuana users hit more pedestrians, exceeded the speed limit more often, made fewer stops at red lights, and made more centerline crossings.
"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."
When researchers divided marijuana users into groups based on when they started using cannabis, they found that significant driving impairment was detected and completely localized to those who began using marijuana regularly before age 16.
Dahlgren said that "research has consistently shown that early substance use, including the use of cannabis, is associated with poorer cognitive performance."
She added, "What was interesting was when we examined impulsivity in our analyses, most of the differences we saw between cannabis users and healthy controls went away, suggesting that impulsivity may play a role in performance differences."
States where marijuana has been legalized have seen growing public concern that more individuals will drive while intoxicated. But since performance issues can occur even in people who aren't high, Gruber said the public needs to rethink the ways it understands impairment.
Dahlgren concluded that "it's important to be mindful that whether someone is acutely intoxicated, or a heavy recreational cannabis user who's not intoxicated, there may be an impact on driving, but certainly not everyone demonstrates impairment simply as a function of exposure to cannabis. This is especially important to keep in mind given increasing numbers of medical cannabis patients who differ from recreational users with regard to product choice and goal of use."