The association between cannabis use and mood disorders: A longitudinal study

Background: The association between cannabis use and mood disorders is well documented, yet evidence regarding causality is conflicting. This study explored the association between cannabis use, major depressive disorder (MDD) and bipolar disorder (BPD) in a 3-year prospective study.

Methods: Data was drawn from waves 1 and 2 of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC). MDD and BPD were controlled at baseline and defined as meeting full criteria in the 12 months prior to the follow-up. Initiation of cannabis use was defined as any cannabis used by former lifetime abstainers in the time period between baseline and follow-up.

Results: Cannabis use was not significantly associated with increased incidence of MDD (Adjusted Odds Ratio (AOR) for daily use=0.58(0.22-1.51)). Weekly to almost daily cannabis use was associated with increased incidence of BPD ((AOR for weekly to daily use=2.47(1.03-5.92)); daily use was not (AOR=0.52(0.17-1.55)). Baseline MDD was associated with initiation of cannabis use (AOR=1.72(1.1-2.69)). A crude association between baseline BPD and incidence of cannabis use was not maintained in adjusted models (AOR=0.61(0.36-1.04)).

Limitations: Lack of information regarding frequency of cannabis use at follow-up and limitations regarding generalization of the results.

Conclusions: Our findings do not support a longitudinal association between cannabis use and incidence of MDD. Results regarding the association between cannabis use and incidence of BPD are conflicting and require further investigation. Baseline MDD, but not BPD, may be associated with future initiation of cannabis use. This may have implications for clinical, social and legislative aspects of cannabis use.