Here is the trick: users handled this badly even when they were no longer drugged.
The study, published Tuesday in the journal Drug and Alcohol Dependence, asked chronic and heavy marijuana users to drive in a personalized driving simulator.
“Intensive use was defined by daily or near daily use, a minimum of four or five times a week, with a lifetime exposure of 1,500 times,” said Staci Gruber, director of the Marijuana Research program for neuroscientific discovery ( MIND) at McLean Hospital. , the largest psychiatric teaching hospital at Harvard Medical School.
At the time of the driving experience, the marijuana group had not consumed for at least 12 hours and, according to urine tests, they were not intoxicated with THC, the main psychoactive compound in recreational marijuana.
Despite not having THC in their system, heavy users always performed worse in handling tasks than non-users, making critical and dangerous mistakes.
The worst drivers? Those who started using regularly before the age of 16.
“Before the age of 16, the brain is especially vulnerable to neurological development, not only to cannabis but to other drugs, alcohol, diseases and injuries,” Gruber said. “The brain is really under construction, or if you are in the world of cannabis, ‘halfway.’
“And when we look at cannabis users and separate them in early use (before age 16) compared to later onset, almost exclusively these differences between the two groups were attributed to the early-onset group,” said Gruber. “So, it is early cannabis exposure that seems to confer greater difficulty with complex cognitive tasks such as driving.”
That was no real surprise, said study co-author Mary Kathryn Dahlgren, a postdoctoral fellow at MIND.
“Research has consistently shown that early substance use, including cannabis use, is associated with poorer cognitive performance,” said Dahlgren, “specifically tasks controlled by the most frontal part of the brain, the part behind the eyebrows. “.
That is also the part of the brain that controls our impulses, an important factor in appropriate behavioral choices.
“We have documented the role of impulsivity in cannabis users before, and it seems that earlier onset may confer a diminished ability to inhibit inappropriate responses,” Gruber said, adding that science does not fully understand the relationship.
“What comes first? Are these impulsiveness differences that drive early cannabis use? Is it early cannabis use that drives impulsiveness differences? That question really needs to be addressed in future longitudinal studies that analyze these people before they start using cannabis. “
Does this same concern apply to medical marijuana users? Not at all, says Gruber.
“In our patients with medical cannabis we don’t see that at all. In fact, we see improvements,” he said.
But both Gruber and Dahlgren emphasize that it is too early to say how significant these results can be.
“In no way do these data suggest that all people who use cannabis are damaged, they cannot drive,” said Dahlgren. “But we must take into account our younger and more vulnerable consumers with regard to the age they are exposed to and may begin to use regularly, because there may be later effects of that use later.”
That is especially worrying given the fact that the herb seems to be replacing cigarettes in recent national surveys, Gruber said.
“The daily consumption of cigarettes among 12th grade students was 2.4% and the use of marijuana was 6.4%,” he said. “Do you remember the entire campaign with Nancy Reagan, ‘Just say no’ and how it didn’t work? Then we say to teenagers, ‘Just not yet.’ Give your brain more time and opportunity to develop before using.”