L-TRYPTOPHAN is an essential amino acid that serves as a precursor for the sleep hormone melatonin as well as for niacin and serotonin. Serotonin is an important neurotransmitter in the central nervous system that has a calming effect and modulates anger, aggression, temperature, mood, sleep, sexuality, appetite and metabolism. L-Tryptophan is the least abundant amino acid in the American diet. Even a person on a high protein diet generally gets less than 1.5 grams a day. Supplementary L-Tryptophan may provide nutritional support for restful sleep and a positive mood.