I've only done one fast so far (I'm planning on starting a longer one tomorrow, actually). It lasted 15 days, but was supposed to be 28. I stopped because the mental effects were so intense. I think I was fine until the start of the second week and then I would get really hostile. I think I just felt left out and it made me kind of depressed. Then the night before I ended my fast, I had these horrible racing thoughts all night long. And it was all about food. I could not stop thinking about food. It started to freak me out. I hope it's different on my next fast. But I've never been on any kind of medication, except for the bc pill which was a short while long before my fast.