Cannabis Use and Internalizing/Externalizing Symptoms in Youth: A Canadian Population-Based Study

With the recent legalization of cannabis for nonmedicinal purposes in Canada, it is becoming increasingly important to understand the potential mental health risks that cannabis may present. The objective of this study was to estimate associations between the frequency of cannabis use and the presence of elevated internalizing (e.g., anxiety and depression) and externalizing (e.g., conduct disorder and attention deficit hyperactivity disorder) symptoms within Ontario youth aged 12-17 years.

The 2014 Ontario Child Health Study included Emotional and Behavioural Scales used to assess internalizing and externalizing symptoms. To assess associations between internalizing/externalizing symptoms and cannabis use, the Ontario Child Health Study-Emotional and Behavioural Scales were dichotomized using the upper quintile (those with the most severe symptoms). Logistic regression was used to estimate odds ratios (ORs) to quantify the association between the frequency of cannabis use and the presence of elevated internalizing and externalizing symptoms. Estimates used a recommended procedure (replicate bootstrap weighting) to address design effects.

A significant association between frequent cannabis use and elevated externalizing symptoms was observed with an OR of 2.17 (1.80-2.62) in males and 5.13 (4.24-6.21) in females. Similar significant associations were also observed between frequent cannabis use and elevated internalizing symptoms with an OR of 2.07 (1.74-2.47) in males and an OR of 3.40 (2.73-4.24) in females. These associations were still present after adjusting for age, binge drinking, smoking, and negative/positive parenting.

Cannabis use, especially in females and frequent users, is associated with elevated levels of internalizing and externalizing symptoms.