By Teens who start using cannabis before age 15 are more likely to use it frequently in later adolescence — and those who start early and use regularly face higher rates of both physical and mental health problems in early adulthood, according to a new study published in JAMA Network Open.
“This further builds the case that cannabis use in adolescence adversely affects the [health] trajectories of those who use it,” said Dr. Ryan Sultan, a psychiatrist at Columbia University who was not involved in the study.
Large Canadian cohort followed from infancy to young adulthood
The findings come from the Müller Longitudinal Study of Child Development, a long-running project in Montreal, Canada, that has followed more than 1,500 children from infancy into early adulthood to identify factors that shape their development and health. Researchers documented many aspects of the participants’ lives — including cannabis use between ages 12 and 17 — along with family dynamics, peer relations and other potential influences on health.
According to the analysis:
- 60% of adolescents did not use cannabis during their teen years.
- Of the remaining 40%, roughly half began using cannabis in their late teens and were using it less than once a month by age 17.
- The other 20% began using before age 15 and were using cannabis at least once a month by age 17.
Early, regular users show higher rates of medical care for health problems
Compared with adolescents who did not use cannabis, those who started early and used frequently were significantly more likely to seek medical attention for both mental and physical health problems in early adulthood. After accounting for a wide range of potential confounding factors — including bullying and a lack of parental involvement — the researchers report:
- 51% higher likelihood of receiving treatment for mental health problems among early and regular cannabis users versus non-users.
- 86% higher likelihood of requiring medical attention for physical health problems in the same comparison.
Dr. Massimiliano Orri, a psychologist at McGill University and the paper’s lead author, summarized the pattern: “The risk is concentrated among those who start early and use frequently.”
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Most-reported physical harms and possible mechanisms
The study authors and outside experts note several candidate explanations for the increase in physical health visits. Orri and colleagues observed that respiratory problems were among the most frequently reported physical complaints, alongside accidents and unintentional injuries. The team suggests these outcomes might be related to cannabis intoxication (acute impairment) or to withdrawal symptoms experienced when use is reduced or stopped.
“That certainly makes sense,” said Dr. Krista Lisdahl, a psychologist at the University of Wisconsin–Milwaukee, who was not involved in the study. She added that the study’s careful control for confounders — family structure, parental conflict, parenting style, parental monitoring, social skills, peer interactions and peer mistreatment — is a major strength. “The fact that Orri and his colleagues controlled for so many confounding factors is a major strength of the study,” Lisdahl said.
Early cannabis use and mental-health risks — how big is the danger?
This new analysis joins prior work linking adolescent cannabis use to later mental-health problems. Dr. Ryan Sultan highlights the magnitude observed in other research: recreational cannabis users in youth may have two to four times the risk of developing psychiatric disorders compared with non-users. Other studies have found an association between early cannabis use and adolescent-onset psychosis, and researchers have also reported links with school problems such as truancy and poorer grades.
Experts emphasize a plausible developmental mechanism: the adolescent brain remains highly dynamic well into young adulthood, and regular exposure to psychoactive substances during this period could disrupt healthy maturation — especially in brain regions responsible for executive function (planning, problem solving and impulse control) and emotion regulation.
“The adolescent brain is continuing to develop in a very dynamic fashion during the adolescent period and all the way into young adulthood,” Lisdahl said. “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… but also emotion regulation.”
Dr. Sultan offered a clinical example: an anxious adolescent who uses cannabis to calm nerves may come to rely on the drug as a coping strategy. “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.” The same pattern holds for anyone using cannabis to regulate mood.
Practical guidance from clinicians
Because early and frequent cannabis use appears to concentrate risk — particularly for youth already vulnerable to mental-health symptoms — some clinicians counsel strong delay. Sultan, who treats children and adolescents, said he often advises parents and teens to postpone cannabis use until age 25 in order to reduce the likelihood of later behavioral and health problems.
Bottom line
- A long-term Canadian cohort study found that adolescents who begin cannabis before age 15 and use it at least monthly by age 17 are more likely to require medical care for both mental and physical health problems in early adulthood.
- These early, regular users had a 51% higher chance of mental-health treatment and an 86% higher chance of physical-health treatment compared with non-users — findings that held after adjusting for numerous family and social confounders.
- Respiratory complaints, accidents, and potential intoxication/withdrawal effects were among the implicated physical harms; prior research also links early use with increased risk of psychiatric disorders, poorer school outcomes, and possible links to psychosis.
- Experts stress that adolescence is a sensitive period for brain development; delaying cannabis use can reduce the likelihood of long-term harms.
