A dose-response association, suggesting that heavy cannabis users are more likely to report depressive disorders, has been hypothesized. However, evidence is not conclusive, and we aimed at testing the existence of a linear association between different levels of cannabis use and depressive disorders using large, representative, repeated surveys.
We examined prevalence rates of different levels of past-year cannabis use and major depressive episode (MDE), separately for young people (12-17 years) and adults (18-64 years), using data between 2006 and 2015 from the National Survey on Drug Use and Health. Prevalence rates estimates with 95% confidence intervals were computed, and the association between past-year MDE and cannabis use was assessed. We then investigated whether time-period trends existed for MDE and, if so, whether these differed by cannabis use levels. Models included both time period, to evaluate trend changes in past-year MDE from 2006 to 2015, and time period by cannabis level interaction terms.
Cannabis users were more likely, using both single-year and pooled survey data, to have suffered from MDE in the past year. Multiple logistic regression models, after adjusting for time period, age, and gender, showed an association between MDE and cannabis use, regardless of its levels. However, a roughly dose-response relationship was detectable only for adults. Trends in past-year MDE prevalence rates among subjects with different levels of cannabis use did not differ from trends among nonusers. Women were more likely to report concurrent past-year MDE and cannabis use than men.
Cannabis users have consistently higher prevalence rates of depressive disorders compared with nonusers, suggesting the need for integrated screening and treatment programs to tackle this comorbid condition.