A new study led by researchers at McGill University has found that using cannabis from an early age—especially before 15 years old—and using it frequently can increase the risk of both mental and physical health problems in young adulthood.
The researchers discovered that teens who begin using cannabis before turning 15 and continue using it daily or almost daily are more likely to seek medical help later for mental health problems like depression, anxiety, and suicidal thoughts.
They are also more likely to experience physical health issues such as breathing difficulties and injuries. On the other hand, teens who begin using cannabis after age 15 mostly faced physical health problems but not the same level of mental health issues.
These findings suggest that the age at which young people begin using cannabis, as well as how often they use it, matters a lot for their future well-being. The researchers published their findings in the journal JAMA Network Open.
Cannabis is often seen by young people as a harmless or even helpful substance, but the study shows that its effects can be serious—especially for younger teens. One possible reason is that brains under the age of 15 are still developing rapidly.
This stage of brain growth may make teens more sensitive to the effects of cannabis, especially on mental health. According to Massimiliano Orri, Assistant Professor of Psychiatry at McGill University, this could explain why earlier users are at higher risk for emotional problems.
There are also many different ways cannabis might be connected to mental and physical health. For some, cannabis may be used to escape or cope with problems they already have. For others, it might create new problems.
Orri also mentioned that cannabis can make people less focused and more distracted, which may increase the risk of accidents and physical injuries.
The study used data from the Quebec Longitudinal Study of Child Development. This data followed thousands of young people between the ages of 12 and 17 and examined their cannabis use over time.
Researchers then linked this data to health care records to see what happened as these young people reached the age of 23. They took into account a number of early-life factors—like family environment and how often the teens used health care before—so they could focus on cannabis’s specific effects.
Pablo Martínez, a postdoctoral fellow at McGill, noted that even when they adjusted for these early factors, they still found clear signs that early and frequent cannabis use was linked to more health problems. This strengthens the idea that cannabis itself may be playing a direct role.
This research provides new evidence for the ongoing discussion about when cannabis use becomes risky. It supports current public health recommendations that young people should avoid using cannabis until they are older.
Although cannabis is now legal in Canada, the rules vary by province. Quebec has the strictest law, setting the minimum age to buy cannabis at 21, while the federal government allows it from 18, and most provinces set it at 19.
However, legality is only one piece of the puzzle. Changing social attitudes and easier access since legalization mean some teenagers may still be tempted to try cannabis early.
Orri emphasized the importance of public health campaigns focused on identifying young people who are at higher risk of starting cannabis early and using it heavily. These teens could benefit from early support and guidance to reduce their long-term risks.
Overall, this study sends a clear message: delaying cannabis use could protect teens from a range of future health issues. Understanding when and how cannabis becomes harmful is key to protecting the next generation.
If you care about heart health, please read studies about heart disease hidden and essential vitamins for heart health: a guide to a healthy heart.
If you care about heart health, please read studies about the stuff in your mouth that can increase heart attack risk and statin alternative lowers risk of heart disease as well as cholesterol levels.
The study is published in JAMA Network Open.
Copyright © 2025 Knowridge Science Report. All rights reserved.
