The essential amino acid L-tryptophan is the precursor of the neurotransmitter serotonin and niacin (vitamin B3) and plays an important role in serotonin melatonin metabolism. Ingredients: L-tryptophan, modified cellulose (capsule shell) Recommended dosage: Take one capsule daily with plenty of liquid before a meal Naturvit® Tryptophan 500mg is lactose-free, gluten-free, sugar-free and vegan.