- A new study found that frequent cannabis users who began using prior to the age of 16 appeared to drive differently than those who didn’t use marijuana or those who began using it later in life.
- During a driving simulator test, those who began using before the age of 16 hit more pedestrians, missed more stop signs and red lights, and spent more time speeding.
- Researchers insist that their findings are not translatable to all marijuana users. Nor does their study suggest that early-onset marijuana users appear to actually be impaired even when they aren’t smoking.
- The larger conclusion of their research is that the age at which an individual begins using cannabis is important and can have far-reaching effects on cognition.
Getting stoned and driving is never a good idea, but now new research suggests that for some heavy marijuana users, the drug can negatively affect performance on the road even if they haven’t smoked.
In a driving simulator test conducted by researchers at McLean Hospital at Harvard University, heavy users who began using marijuana prior to the age of 16 hit more pedestrians, missed more stop signs and red lights, and spent more time speeding than nonusers and individuals who began using marijuana later in life.
The research highlights not only some of the potential dangers of marijuana for operators of motor vehicles even if they aren’t acutely high, but also furthers an ongoing discussion about the effects of the drug on the brains of adolescents.
The overwhelming conclusion of the study, published Tuesday in the journal Drug and Alcohol Dependence, is that the age of onset of use of cannabis is associated with poorer driving performance.
“Individuals who use cannabis look different from those who don’t in regard to their driving performance, but more importantly, almost exclusively, the difference between users and nonusers is attributed to the early-onset group,” said Staci Gruber, PhD, one of the study authors and director of the Cognitive and Clinical Neuroimaging Core and the Marijuana Investigations for Neuroscientific Discovery (MIND) program at McLean Hospital.
“It basically extends what we’ve already reported and underscores the importance of the role of age of onset of use in recreational cannabis consumers,” she added.
For the study, Gruber and her team recruited 45 individuals. Twenty-eight were considered heavy cannabis users, which was defined as daily or near daily use, with a minimum of four to five times per week and 1,500 or more lifetime exposures.
Since researchers wanted to test for residual effects of marijuana use on driving performance, they used questionnaires and urine tests to establish that the cannabis users hadn’t used marijuana for at least 12 hours before administering the driving test — that is, they weren’t stoned at the time of the test.
Despite having abstained for half a day, early-onset cannabis users’ performance was worse than that of nonusers and late-onset cannabis users.
“What we’re seeing are small but significant differences in performance where the early-onset users are showing an increased risk of having collisions, missing stop signs, missing stops at red lights, and spending more time over the speed limit,” said Mary Kathryn Dahlgren, PhD, co-author of the study and a postdoctoral research fellow at McLean Hospital, Harvard Medical School.
However, Dahlgren and Gruber insist that their findings aren’t translatable to all marijuana users. Nor does their study suggest that early-onset marijuana users appear to actually be impaired even when they aren’t smoking.
“We’re not ever saying that any of these folks are ‘impaired’ at a clinical level, like, ‘Oh my god, they should be off the road.’ We’re saying when they are not acutely intoxicated, we see differences in those who use and those who don’t, specifically among those with early onset,” said Gruber.
Other experts were quick to pick up on that distinction.
“Differences in driving style should not be conflated with driving impairment,” said Paul Armentano, the deputy director of NORML (National Organization for the Reform of Marijuana Laws).
Armentano points out that other
“That said, no one advocating for adult-use cannabis regulations is opining that young people use or have easy access to cannabis, just the opposite. Regulating adult-use access is a way to impose necessary controls to the cannabis market so that society can better limit and discourage young people from misusing cannabis,” he told Healthline.
“It has long been a principle of NORML to discourage anyone from operating a motor vehicle under the influence of any substance,” he added.
As marijuana legalization has spread from state to state, researchers have struggled to quantify its effects related to motor vehicle outcomes: things like rates of DUI and car accidents. Studies have sometimes come to opposite conclusions.
Gruber and Dahlgren point out that the larger conclusion of their research is that the age at which an individual begins using cannabis is important and can have far-reaching effects on cognition.
“The brain continues to develop throughout the second and into the third decade of life. So the brain is still ‘under construction,’ or in the cannabis world ‘half baked.’ So 21 is [a] way better [age] than 18, which is way better than 14 or 15, for sure. As you age the brain is less vulnerable,” said Gruber.