Actually have tried both l-tryptophan and 5htp - my experience re gut was that l-tryptophan was the one that caused severe constipation to such an extent that i had to get off while 5htp seems to have helped my gut to remain regular and perhaps also IBS. On the other hand even tho i am feeling better with mind alert on 5htp which i am now on at 250mg's spread out with meals, for my FM, i am concerned in that a Dr. Harris on internet had put forth arguments that it serotonin in the gut as in 5htp as it changes in the blood/liver, causes heart valve damage. This is causing a lot of consternation as this 5htp has produced some good days for me for first time in 15 years. Ron