Alright, this is my theory on how ssri antidepressants work to "treat depression"
One of the most common side effects of ssri's is a decreased sex drive. I believe repressed sexuality is an important factor in the cause of many people's depression/anxiety and anger.
So when you take ssri's you lose your sex drive and therefore you stop repressing it, as the drug more or less removes it.
So SSRI's = decreased sex drive = less repression of sexuality = less anger/frustration = less depression = "happiness"