The essential amino acid L-tryptophan helps support relaxation, restful sleep, and a positive outlook. It play a part in the synthesis of both melatonin and serotonin, hormones involved with mood and stress response. This tryptophan includes the activated coenzyme from of vitamin B-6, called P-5-P, that is required to convert tryptophan to serotonin. L-Tryptophan also support immune functions because it is the body''s precursor to the kynurenines that regulate immunity. If needed, L-tryptophan converts to niacin in the body, which supports circulation, a healty nervous system, the metabolism of food, and the production of hydrochloric acid for the digestive system. Source Naturals L-Tryptophan is extremely pure and is regularly tested to ensure the highest standards of quality.