5-HTP works in much the same way as fluoxetine (or Prozac to give it its trade name).
Solgar Healthnotes Search
gives a good run-down of how it works. I bought some a few months ago, but haven't taken any yet as, when I clicked 'BUY' I hadn't seen the bit about not taking with fluoxetine, which makes a lot of sense when you understand how it works.
In terms of suppressing appetite, it does depend a little on why you feel you may want to suppress your appetite. A bit 'chicken and egg' you might say. When I started taking fluoxetine I did find my appetite was suppressed, more specifically my urge to overeat or binge-eat was suppressed. I do know that this response varies from person to person though, and the reverse can be true in just as many cases.
Prozac in large doses is used by Doctors to control and treat bulimia.
Fluoxetine is fine with CD, but you'd be well to chat it through with your Doctor, and in any event, s/he would need to prescribe it for you.
I wouldn't take St John's Wort as it interferes with the body's absorption of the pill. 5-HTP works slightly differently, but again, I think you should talk to your GP first. If you are suffering with depression there are lots of things that can help but please don't take anything like this if it is just your appetite you want to suppress. REmember it has the reverse effect in some people!
There's a great Solgar supplier just around the side of Brown Thomas in Dublin, Wicklow Street I think, where they have some very knowledgeable staff. If it is just your appetite you want to suppress, you might look at the mineral Chromium which is great for balancing blood sugars - often a cause of overeating. That has some great effects and you should go for a good brand like Solgar (and no, I don't work for them!!)
Sorry about the essay here - I've been working with my own depression and related eating 'issues' since April and if you want to PM or email me to 'talk' further, that'd be grand.