I started taking fluoxetine a few months ago and I will go as far to say that it is the reason I am still alive (I was about to kill myself). I had not been prescribed it; I just somehow got it.
I stopped it, and my old depressed, bipolar self came back after about a week of stopping. So I have started taking it every other day, and that on a smaller dose (10mg).
This makes me wonder how much we are a result of the billions of simple chemical-electrical processes in our brain.