Adolescence is a time of rapid change, experimentation, and, for some, risky choices that can echo into adulthood. One such choice—using cannabis early and often—has come under renewed scrutiny with the release of a major new study led by researchers at McGill University and published in JAMA Network Open on October 29, 2025. The findings are stirring debate among scientists, health professionals, and parents alike, as they shed light on the long-term consequences of early cannabis use on both mental and physical health.
The study, based on data from the Québec Longitudinal Study of Child Development, followed more than 1,500 children from birth into young adulthood. The research team, led by psychologist Massimiliano Orri at McGill, aimed to untangle the complex web of how adolescent cannabis use shapes health trajectories later in life. Their conclusion? The earlier and more frequently teens use cannabis—especially before age 15—the greater their risk for a slew of health problems down the line.
According to the study, 60% of the teens tracked did not use cannabis during adolescence. Of the remaining 40%, half began experimenting in their late teens, using the drug infrequently—less than once a month by age 17. But it’s the other half that’s raising alarms: these young people started using cannabis before they turned 15 and, by age 17, were using it at least once a month.
It’s this group, the early and frequent users, who were found to be significantly more likely to seek health care for both mental and physical issues as they entered young adulthood. "The risk is concentrated among those who start early and use frequently," Orri told NPR, summarizing the crux of the findings. In fact, these early users had a 51% higher chance of seeking care for mental health problems—including depression, anxiety, and suicidal thoughts—compared to their peers who didn’t use cannabis as young teens. The risk for physical health problems was even starker: an 86% higher chance of needing care, with issues such as respiratory problems and accidental injuries topping the list.
What makes these findings particularly compelling, as noted by psychologist Krista Lisdahl of the University of Wisconsin, Milwaukee, is the study’s rigorous approach. Orri and his colleagues didn’t just look at cannabis use in isolation; they controlled for a host of confounding factors known to influence health, like bullying, parental involvement, family conflict, and even peer relationships. "There are a lot of factors that are co-linked with physical health as well as mental health," Lisdahl explained to NPR, emphasizing that the researchers accounted for these variables in their analysis.
But why does early cannabis use have such a pronounced effect? Experts point to the unique vulnerability of the adolescent brain. As Orri told McGill University’s Health e-News, "Youth under 15 are in a critical period of brain growth, which may make them more susceptible to cannabis’s effects on mental health." Lisdahl echoed this point, noting that the adolescent brain is still developing in dynamic ways well into young adulthood. "Using something like cannabis regularly during this period might disrupt that healthy neural development, especially in areas of the brain that are related to executive functioning, which is like problem-solving, planning, maybe controlling other kinds of behaviors and impulses, but also emotion regulation," she said.
Dr. Ryan Sultan, a psychiatrist at Columbia University who was not involved in the study, sees the findings as part of a growing body of evidence linking adolescent cannabis use to adverse outcomes. "This further builds the case that cannabis use in adolescence adversely affects the [health] trajectories of those who use it," Sultan told NPR. His own research has found that teens who use cannabis recreationally are two to four times more likely to develop psychiatric disorders compared to those who abstain.
The consequences aren’t limited to mental health. The McGill study found that physical health problems among early, frequent users often included respiratory issues—likely linked to the act of smoking cannabis—as well as accidents and unintentional injuries. Orri and his colleagues speculated that these problems could stem from both intoxication and withdrawal symptoms. "We have some indication that respiratory problems were most frequently reported and also accidents and unintentional injuries," Orri explained.
Importantly, the study found that starting cannabis use after age 15 was linked only to more physical health problems later in life, not the mental health issues seen in those who started younger. This distinction, say experts, underscores the particular risk that early adolescence poses. The brain’s heightened plasticity during this period may leave it especially vulnerable to substances that alter neural development.
But the story doesn’t end with biology. Social and behavioral factors play a crucial role as well. Sultan pointed out that teens who use cannabis to manage anxiety or mood may become reliant on the drug as a coping mechanism, at the expense of developing healthier strategies. "If you start to do that on a regular basis, this is now your method for managing your anxiety," he said. "This becomes your coping skill and you become atrophied in any ability to manage it in another way." Over time, this reliance can entrench mental health symptoms and make recovery that much harder.
For parents and policymakers, the findings present a clear, if daunting, challenge. With cannabis becoming more accessible in many parts of North America, the temptation for teens to experiment is only likely to grow. Sultan, for one, now routinely counsels teens and their families to delay cannabis use until age 25, when brain development has largely stabilized. The rationale is simple: the longer young people can wait, the lower their risk of encountering serious health problems later.
Yet, as with any public health issue, there are no simple solutions. Some advocates argue that focusing solely on the risks of cannabis may overshadow the importance of education, harm reduction, and support for young people already using the drug. Others worry that alarmist messaging could backfire, pushing conversations about cannabis use underground and making it harder for teens to seek help when they need it.
What’s clear is that the conversation around adolescent cannabis use is evolving, shaped by new research and real-world experiences. As more studies emerge, the hope is that parents, educators, and health professionals will be better equipped to guide teens through the tricky terrain of growing up in a world where cannabis is increasingly normalized—and, for some, fraught with hidden dangers.
In the end, the McGill-led study serves as a wake-up call: the choices made in adolescence can have ripple effects for years to come. And while the debate over cannabis will no doubt continue, the evidence suggests that when it comes to starting young and using often, the risks are simply too high to ignore.