Tryptophan is an essential amino acid; therefore, it is not synthesized by the body and must be obtained from the diet. 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. Every lot of NOW L-Tryptophan is tested to be free of peak E and microbial contamination. Natural color variation may occur in this product.