The essential amino acid L-tryptophan helps support relaxation, restful sleep, and a positive outlook. It plays a part in the synthesis of both melatonin and serotonin, hormones involved with mood and stress response. This tryptophan includes the activated coenzyme form of vitamin B-6, called P-5-P, that is required to convert tryptophan to serotonin. 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-Tryptophan is extremely pure and is regularly tested to ensure the highest standards of quality.