The association between lifetime cannabis use and dysthymia across six birth decades.

Background: Though high rates of co-occurring cannabis use and depression are well-documented, data regarding the association between cannabis use and dysthymia is scarce. The aim of this cross-sectional study was to explore clinical correlations of cannabis use among individuals with dysthymia, as well as the changes in the association between cannabis use and dysthymia across six decades of birth cohorts.
Methods: Data were drawn from the National Epidemiologic Survey on Alcohol and Related Conditions-III (NESARC-III; 2012-2013; N = 36,309). Participants were divided into six birth cohorts (1940s-1990s), based on their decade of birth, and individuals with dysthymia were further categorized by 3 levels of lifetime cannabis use: non-users, non-CUD users, and CUD-users. We compared rates of co-occurring psychiatric and substance use disorders among cannabis users vs non-users and conducted logistic regression analyses in order to determine the odds of dysthymia among cannabis users across six decades.
Results: Rates of several psychiatric disorders, such as personality disorders, and substance use disorders were higher among individuals with dysthymia who used cannabis compared to those who did not. The interaction between cannabis use (without a CUD) and birth cohort was associated with a decrease in the odds of dysthymia (OR=0.90, 95% CI 0.84-0.97) and remained significant after controlling for confounding variables. Similar changes over time were not demonstrated for CUD users.
Limitations: Likelihood for recall bias and misclassification based on cross-sectional nature of the study and on respondents' self-reports of symptoms throughout their lifetime.
Conclusions and Implications: Our study's findings demonstrate that the association between cannabis use (but not CUDs) and dysthymia has weakened over time. These findings highlight the need for further research examining changes over time in the relationship between cannabis use and associated psychiatric disorders.
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