I was having terrible IBS symptoms along with extreme anxiety. I started taking 5-htp on the advice of my naturopathic doctor. Within 1-2 weeks, my IBS reduced substantially and my anxiety lessened dramatically. I felt great everyday with a more stable, consistent mood than I have ever felt in my life.
According to my doctor, a large proportion of serotonin either resides or is made in your gut (I forget which) so it makes sense that it helped my IBS. When I started, I was taking 200 mg each morning. It didn't help me sleep though, in fact it kept me wide awake. After taking for about a year or so, I started feeling very ill every morning. It took me a long time to figure out it was the 5-htp. However, my general health has improved much over the past year and I have now cut the dose back to 50 mg per day and can handle it fine. My doctor told me my system probably did not need as much now and this is perhaps why larger doses were making me so ill.