The essential amino acid l-tryptophan helps support relaxation, restful sleep, and positive mood. It plays a part in the synthesis of both melatonin and serotonin, hormones involved with mood and stress response and sleep/wake cycles. l-Tryptophan also supports 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 healthy nervous system, the metabolism of food, and the production of hydrochloric acid for the digestive system. Source Naturals l-Trtptophan is extremely pure and is regularly tested to ensure the highest standards of quality.