A study done in Sweden spanning 35 years and testing a total of 45,087 Swedish men has found no connection linking cannabis and depression.
That being said, although the risk was extremely slight, the study did reiterate the connections found between chronic cannabis use and schizoaffective disorders. The study finds that “there was a strong graded association between cannabis use and schizoaffective disorder, even after control for confounders, although the numbers were small (HR 7.4, 95% CI, 1.0-54.3).
“Conclusion: We did not find evidence for an increased risk of depression among those who used cannabis. Our finding of an increased risk of schizoaffective disorder is consistent with previous findings on the relation between cannabis use and psychosis.”