Weed Affects Driving Skills Way Longer Than Previously Thought

Drunken drivers may not be the only ones responsible for road accidents. Marijuana users also demonstrated equally poor driving skills, even when they were not intoxicated, as per a new study published in the journal Drug and Alcohol Dependence

There is a growing concern that the number of accidents involving people intoxicated with marijuna is on the rise, especially since data reflects the surge: fatal crashes with junkies increased from 8 percent in 2013 to 17 percent in 2014. Researchers at the Marijuana Investigations for Neuroscientific Discovery (MIND) program at McLean Hospital, the psychiatric teaching hospital of Harvard Medical School, examined the driving performance of heavy users of recreational marijuana in a controlled study. 

Customized driving simulators were driven by the group comrpised of generally heavy users of the substance but were not intoxicated in the last 12 hours. The driving test results were then compared to subjects who never abused marijuana, either recreationally or medically. 

This is the first time a study was looking at users who were not under the influence during rash driving. It found that it was the residues left behind in their bodies that contributed to some of the road mishaps. In the past, studies have proven that severely intoxicated marijuana users were associated with impaired driving, but not in this study. 

After taking everything into account, frequent marijuana users demonstrated poorer control over the vehicle during the simulated driving test in comparison to the healthy participants. What exactly was wrong with the driving of habitual pot smokers? They were prone to accidents on the road, they hit some pedestrians by not stopping at the crosswalks and had lateral movement. They also did not follow all the traffic rules, especially by sometimes not halting at the signals.

Marijuana A picture taken on June 5, 2019 shows a man smelling a sample of Marijuana buds, often simply called weed or pot, which is the unprocessed form of the female cannabis plant, at the "Hemp Embassy" store in Milan, one of the first shops in Italy dedicated to cannabis. MIGUEL MEDINA/AFP/Getty Images

 "People who use cannabis don't necessarily assume that they may drive differently, even when they're not high," Staci Gruber, director of the MIND program and senior study author,  pointed out.

"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 explained. 

Furthermore, the participants were divided based on the age at which they started using the substance. It was found that significant driving impairment was restricted to people who had started using pot before the age of 16, especially in stark comparison to those who started using pot later than 16. 

Impulsivity displayed by the participants had a role to play in impaired driving, suggesting that frequent users developed aggressive behavior. “Further, covariate analyses suggest that impulsivity had a significant impact on performance differences,” the authors stated in the paper. 

However, even the healthy control group sometimes surprisingly displayed impulsivity. “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," Mary Kathryn Dahlgren, study co-author and a postdoctoral fellow at MIND, explained. 

On the contary, the researchers emphasized that people who take medicinal cannabis need not necessarily be involved in a road accident. “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," Dahlgren added.