I have been reading through a new paper on magnesium and depression. The authors believe that magnesium will help those with treatment-resistant depression, and even all subjects with depression. This follows up on earlier studies with similar results.
This study found that women with the lowest serum magnesium levels were more likely to have mood disorders. This study found that higher intakes of magnesium correlated with lower levels of depression.
Overall, this looks promising that an inexpensive over-the-counter supplement could help with depression.