Marijuana use and the risk of Major Depressive Episode. Epidemiological evidence from the United States National Comorbidity Survey

Background. This is an epidemiological study of a possible causal role of marijuana use in the development of Major Depressive Episode (MDE). Male-female differences in the suspected causal association have also been studied. Method. Data are from 6,792 National Comorbidity Survey participants aged 15-45 years, assessed via the University of Michigan modified version of the Composite International Diagnostic Interview (UM-CIDI). Survival analysis methods were used to estimate cumulative risk of MDE by levels of marijuana use and to estimate suspected causal associations after adjustment for other influences. Results. The risk of first MDE was moderately associated with the number of occasions of marijuana use and with more advanced stages of marijuana use. Relative to never users, non-dependent marijuana users had 1.6 times greater risk of MDE (95% Confidence Interval: 1.1, 2.2), even with statistical adjustment for sex, birth cohorts, alcohol dependence, and history of daily tobacco smoking. Conclusions. There was male-female variation in the degree of association between stage of marijuana involvement and MDE, but the strength of the association is modest at best.