A new study has shown that people who start smoking cannabis on a frequent basis before the age of 16 tend to be worse drivers later in life than those who abstain from the drug- even when they’re not high.

To conduct the research, researchers at McLean Hospital in Belmont recruited 45 healthy participants to complete a 4.2 mile virtual course using a driving simulator. Of those in the cohort, 17 did not smoke marijuana while 14 consumed the drug heavily from before the age of 16, and 14 started smoking later in life. The virtual course included stop signs, traffic lights, yields, merges, pedestrians and other vehicles. Each participant was graded on their ability to follow traffic rules, stay in their own lanes and their responses to sudden obstacles and potential dangers.

For the study, those defined as “heavy” smokers had consumed cannabis for five out of the previous seven days prior the simulator, were said to have smoked at least 1,500 times, and tested positive for cannabinoids on biological tests. Prior driving with the simulator, all users had to abstain from the drug for at least 12 hours.

In their results, the researchers found that those who began smoking cannabis before the age of 16 tended to be poorer drivers than those who started later, or who simply abstained from the drug altogether. However, when the researchers controlled for self-reported impulsivity among the participants, they found that differences between the groups in driving performance was less significant, suggesting that impulsivity alone among those in the heavy-smoking group may have accounted for much of the variance in simulator values.

Although the study found something of a correlation between marijuana usage and driving ability, Staci Gruber, one of the study’s leaders, warned against taking her results as evidence against mariuana usage. Given the small sample size of her study, alongside surmounting evidence demonstrating its utility in improving cognitive abilities when used for medicinal purposes, she said, “This doesn’t mean if you put heavy cannabis users on the road they’re going to mow people down and drive horribly — it doesn’t mean they’d hit impaired levels of driving in the real world...It just means there are differences.”



Sources: Boston Globe, 9News and Science Direct