According to longitudinal data published in the online version of the Journal of Affective Disorders, marijuana use is found to not be associated with increased incidences of major depression.
A team of investigators from Israel and Canada studied the association between marijuana use, major depressive disorder (MDD) and bipolar disorder (BPD) during a three-year prospective study and determined that future incidences of MDD were no higher among marijuana users than when compared to nonusers. The authors reported, “Our results show no significant association between cannabis use and the incidence of major depression.”
Contrarily, MDD was associated with increased incidences of marijuana use. The authors concluded, “Our results do not support a longitudinal association between cannabis use and increased incidence of MDD; rather, they indicate an inverse relationship between the two, which may be attributed to self-medication factors.”
The full study, “The association between cannabis use and mood disorders: A longitudinal study,” can be found online in the Journal of Affective Disorders.