New research said that the use of marijuana can affect the person's driving ability up to 12 hours after taking it. The study was published in Drug and Alcohol Dependence. It said that chronic, heavy recreational user sowed poor driving performance when compared to a non-user. This is the first attempt to understanding the usage differences between a person who is a chronic user and non-user.

"People who use cannabis don't necessarily assume that they may drive differently, even when they're not high," said study researcher Staci Gruber from McLean Hospital in the US.

Marijuana
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"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," Gruber added.

For the findings, the research team 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 for at least 12 hours and were not intoxicated. 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.

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.

"It didn't surprise us that performance differences on the driving simulator were primarily seen in the early onset group," said study researcher Mary Kathryn Dahlgren.

According to the authors, research has consistently shown that early substance use, including the use of cannabis, is associated with poorer cognitive performance.

"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," Dahlgren added.

"There's been a lot of interest in how we can more readily and accurately identify cannabis intoxication at the roadside, but the truth of the matter is that it is critical to assess impairment, regardless of the source or cause," she said. o

"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," she added.

(With inputs from agency)