I take 5-htp for my PMS. It increases the amount of seratonin in the blood stream (similar effect but different method as a SRI drug like Prozac) and keeps me calmer. My PMS is off the charts, and I really don't want to take an antidepressant unless I have to. The 5-htp has helped tremendously (I take 100mg a day) with the PMS and my general stress level..which probably helps my IBS because stress is my biggest trigger!