Starting cannabis use before the age of 15 may set the stage for future health struggles, according to a new study linking early cannabis use to higher odds of both mental and physical health problems in young adulthood.
Around the world, cannabis is one of the most commonly used substances during adolescence. However, adolescence is a critical development period. It’s marked by significant brain development, where the emotional part of the brain develops faster than the region responsible for planning and judgment, which continues to mature into the mid-20s.
New research led by McGill University in Québec, Canada, has examined how starting cannabis use before or after age 15 affects physical and mental health in early adulthood.
“Youth under 15 are in a critical period of brain growth, which may make them more susceptible to cannabis’ effects on mental health,” said senior author Massimiliano Orri, PhD, Assistant Professor in McGill’s Department of Psychiatry and Principal Investigator at the Douglas Research Center. “Cannabis can also impair attention and cognition, which may increase the likelihood of accidents causing injuries.”
The researchers followed 1,591 participants from the Québec Longitudinal Study of Child Development (QLSCD) from birth to age 23. Data sources included participants’ self-reported cannabis use (at ages 12, 13, 15, and 17), plus official medical records for mental and physical health care received between ages 18 and 23.
The researchers identified three usage patterns using group-based trajectory modeling: Non-users (never used cannabis), late-onset users (started after 15, used infrequently), and early-onset, frequent users (started before 15, used often), around 60%, 20%, and 20%, respectively. The models were adjusted for 32 confounding factors, including family background, socioeconomic status, parental substance use, early childhood behavior problems, and preexisting medical issues, to isolate cannabis effects from other influences.
In terms of mental health, frequent cannabis users had 51% higher odds of medical visits for any mental disorder. They had 57% higher odds of treatment for common mental disorders, such as depression and anxiety, for example. Regarding physical health, frequent users had 86% higher odds of care for any physical conditions. They had significantly more visits for injuries and poisoning. The researchers found no clear link to respiratory diseases or suicide-related behaviors.
By comparison, for late-onset cannabis users, the researchers found no significant increase in mental health care needs. There were higher odds of care for physical conditions, especially injuries and poisoning. Non-users, which served as the baseline comparison group, had lower rates of health service use across all categories, as might be expected.
“Even when we considered several pre-existing risk factors for cannabis use, we still found increasing risks of using healthcare services for mental and physical health problems for youth with early-onset cannabis use,” said Pablo Martínez, PhD, the study’s lead author and a postdoctoral fellow at McGill. “That suggests cannabis itself may play a role.”
The authors note several caveats to their findings. First, unmeasured genetic or personality traits could still influence both cannabis use and later health outcomes. Also, males and lower-income participants were more likely to drop out. Medical records don’t capture milder conditions that don’t result in healthcare visits. Underreporting of cannabis use is possible. Finally, the study took place before Canada legalized cannabis (2018), so patterns may differ today with higher-potency products and changing norms.
Nonetheless, the findings add new evidence to the ongoing debate about the safety of cannabis use during adolescence.
“Efforts to steer youth away from consuming cannabis too young are important,” said Orri. “Public health initiatives should focus on identifying young people likely to start early and use frequently, as they may benefit from clinical interventions to reduce long-term risks.”
The study was published in the journal JAMA Network Open.
Source: McGill University
