Association between marijuana and depression: Exploring the mediating role of environmental pollutants

Depression is a widespread mental health disorder that significantly affects both individuals and society. This study aimed to examine the association between marijuana use and major depression among U.S. adults, and to investigate whether environmental pollutants mediate this relationship.

We analyzed data from 21,304 adults aged 20-59 in the 2005-2018 cycles of the National Health and Nutrition Examination Survey (NHANES). Depressive symptoms were measured via the Patient Health Questionnaire (PHQ-9). Urinary polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs) were measured as mediating variables. Weighted multivariable logistic, linear regression and weighted quantile sum regression models were used to assess associations. Mediation analysis was conducted to estimate indirect effects of these pollutants.

Current marijuana use was associated with increased odds of major depression (adjusted OR = 1.99; 95 % CI: 1.57-2.50), independent of sociodemographic, behavioral, and clinical confounders, including tobacco and other drug abuse. Combined marijuana and tobacco use showed the highest risk (adjusted OR = 3.05; 95 % CI: 2.48-3.75). Mediation analysis identified three PAH metabolites-1-hydroxynaphthalene, 2-hydroxyfluorene, and 3-hydroxyfluorene-as partial mediators, accounting for 10.6-17.4 % of the association between marijuana use and depressive symptoms.

Marijuana use is positively associated with depressive symptoms among U.S. adults, and this association is partly mediated by exposure to specific PAHs. These findings underscore the need to consider environmental pollutant exposure in studies of substance use and depressive symptoms.