It's been shown that antidepressants are no better clinically than placebos. The drug companies simply suppressed the trials that didn't yield the results they wanted and cherry-picked the ones that did in order to get FDA approval. This all came out a couple of years ago when a long-running Freedom of Information Act suit forced them to release all the trials.

http://www.guardian.co.uk/society/2008/feb/26/mentalhealth.m...

Edit: I just remembered that I posted about this to HN back when the study came out: http://news.ycombinator.com/item?id=123575. A commenter pointed out that the study was limited to SSRIs, the most widely used antidepressants.