“The present review will provide an overview of the neurobiology, epidemiology, clinical impact, and treatment of cannabis use disorder (CUD) in mood disorders.

Patients with mood disorders including major depressive disorder (MDD) and bipolar disorder (BD) have higher rates of cannabis use, and CUD compared to the general population. Reasons for this association are not clear, nor are the putative therapeutic effects of cannabis use, or its components delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD), in these illnesses.

Cannabis use may be associated mood disorders, but more research is needed to increase our understanding of the mechanisms for this association, and to develop more effective treatments for this comorbidity.”

https://www.ncbi.nlm.nih.gov/pubmed/30643708

https://link.springer.com/article/10.1007%2Fs40429-018-0214-y

“Antidepressant-like effect of delta9-tetrahydrocannabinol and other cannabinoids isolated from Cannabis sativa L. Results of this study show that Delta(9)-THC and other cannabinoids exert antidepressant-like actions, and thus may contribute to the overall mood-elevating properties of cannabis.”   https://www.ncbi.nlm.nih.gov/pubmed/20332000