A 2026 study in the Journal of Psychiatric Research, which reviewed the findings of 55 prior studies, found that approximately 31% of individuals with cannabis use disorder (CUD) had major depressive disorder (MDD). The study, led by researchers in Brazil, also found that approximately 10% of people with MDD had CUD. The researchers concluded that “cannabis use may exacerbate depressive symptoms, while individuals with MDD are at an increased risk of developing CUD.” This study helps to illustrate how marijuana use and depression often exacerbate each other, highlighting why policymakers should further invest in prevention and treatment interventions.