It's anecdotal, but anti-depressants certainly had a positive effect on my depression. However, a large component of my depression was caused by a co-existing anxiety disorder.

I often feel the anti-depressants cured some kind of physical imbalance that led to my anxiety disorder, and thus the ensuing 'curative' notions of anti-depressants might not be directly attributable to any physiological aspect of my depression, but the cause of a large component of my depression...an anxiety disorder.