Adolescents who start using cannabis early and often are more likely to need health care for both mental and physical problems as they enter adulthood, according to a new study led by McGill University researchers.
The study found those who began using cannabis before age 15 and continued daily or near-daily were more likely to seek care for depression, anxiety, suicidal distress and physical conditions such as respiratory problems and injuries. By contrast, starting after age 15 was linked only to more physical health problems later.
While the study does not interpret these associations, researchers say there are likely different reasons behind the mental and physical health findings.
"Youth under 15 are in a critical period of brain growth, which may make them more susceptible to cannabis's effects on mental health," said Massimiliano Orri, Assistant Professor of Psychiatry at McGill, clinician-scientist at the Douglas Research Centre and Canada Research Chair in Suicide Prevention.
The relationship is complex, he added. Some people may use cannabis to cope with existing problems, while for others, the drug may play a role in the development of new ones.
"Cannabis can also impair attention and cognition, which may increase the likelihood of accidents causing injuries," he said.
First study to link cannabis to health care records
With data from the Quebec Longitudinal Study of Child Development, researchers tracked cannabis use in a large cohort between ages 12 and 17 and linked it to health-care records up to age 23. In their analysis, they accounted for a wide range of early-life factors such as the environment children were raised in and how often they needed health care.
"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, postdoctoral fellow at McGill. "That suggests cannabis itself may play a role."
What age is 'too young' for cannabis?
The study adds new evidence to ongoing debates about when cannabis use becomes risky, backing public health advice for young people to delay the use of cannabis.
In Quebec, the legal age to buy cannabis is 21, stricter than the federal minimum of 18 and the age of 19 in most provinces. Researchers caution that beyond legal rules, shifting social attitudes and easier access since legalization can still influence underage use.
"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."
About the study
"Health Service Use Among Young Adults With a History of Adolescent Cannabis Use: A Population-Based Birth Cohort Study" by Pablo Martínez et al., was published in JAMA Network Open. Funding was provided by the Canadian Institutes of Health Research.
