by Mike Roussell, phD, SHAPE Diet DoctorThis supplement is said to suppress appetite, but will it help you lose weight? Probably not, but it depends. 5-hydroxy-L-tryptophan is a derivative of the amino acid tryptophan and is converted to the neurotransmitter serotonin in the brain. What does that have to do with weight loss? Serotonin is a multifaceted neurotransmitter, and one of its roles is impacting appetite. (Have you ever been in a carb-induced coma where your appetite was completely squashed? Serotonin had a hand in that. ...