I've told this story before, but for those who haven't heard it:
I've had migraines since I was 13 and one of the prophylactics for it is anti-depression medication. I've tried several and most had absolutely zero effect on me, including not helping the migraines. Understand that when you spend 3-5 days a month curled up in a ball because of the pain, you're willing to try ANYTHING.
However, they tried me once on Prozac. I started at 10mg I think (maybe 5) for 5 days - nothing, so he had me double it. Within 48 hours I went into a deep chemical depression. It was the most bizarre thing I have ever experienced. I literally felt like a heavy black cloud was over me. I couldn't convince myself to get out of bed, off the toilet, out of my chair, etc. THANKFULLY I knew what was going on, stopped taking the stuff and was fine in another 48 hours. But it really gave me an insight to what people with chemical depression go through.
The doctor said this happens to a very, very small percentage of people who take it for non-depression reasons. It freaked me out so bad that when I fill out medical forms and they ask me what I'm allergic to, I put down Prozac. I don't want someone giving it to me for ANY reason.