NOW Foods L-Tryptophan 500mg 120 Vcaps. L-Tryptophan is an essential amino acid; therefore it is not synthesized by the body and must be obtained from the diet. L-Tryptophan is critical for the production of serotonin and melatonin which help to support a positive mood healthy sleep patterns and proper immune system function. Supplement is dairy free soy free nut free egg free Non - GMO.