Source Naturals L-Tryptophan promotes positive mood, relaxation and sleep. This essential amino acid plays a part in the synthesis of melatonin and serotonin, the hormones involved with mood, stress response and sleep/wake cycles. L-Tryptophan also supports the body's immune system. Contains no yeast, dairy, egg, gluten, soy or wheat. Contains no preservatives, artificial color, flavor or fragrance.