Hello, and thank you for the great question.
For a reduction in the the symptoms of depression, I recommend a very small dose of sativa or, even better, obtaining a vaporizer pen from hmbldt.com which was specifically formulated for depression; it can also be dosed precisely.
There is preliminary research that has shown low doses of cannabis to activate serotonergic neurons, thereby increasing serotonin – and has even been shown to exert potent antidepressant-like properties in the rat forced-swim test (FST).
However, the same study showed that higher doses of cannabis actually reduced serotonergic action from baseline.
Considering the above, it becomes clear that cannabis is best used at the lowest dose and frequency possible to address your depression. There is both scientific and a plethora of adecdotal evidence that heavy cannabis use can lead to the worsening of depression.