The essential amino acid L-tryptophan is the precursor for the synthesis of melatonin and serotonin, a hormone and a neurotransmitter involved with mood and stress response. It helps support relaxation, restful sleep, and a positive outlook. This tryptophan tablet includes vitamin B-6, which is required to convert tryptophan to serotonin. If needed, L-tryptophan is converted to niacin in the body, an important B vitamin. Source Naturals L-Tryptophan is extremely pure and is regularly tested to ensure the highest standards of quality.*