L-Tryptophan Powder, 2 oz, NOW FoodsNOW Foods L Tryptophan Powder Supports Relaxation. Pharmaceutical Grade (USP). Encourages Positive Mood. Promotes Restful Sleep. Vegetarian Product. L Tryptophan is an essential amino acid important in human nutrition for the synthesis of melatonin and serotonin, hormones regulating mood and stress response. L Tryptophan helps support relaxation, sleep, positive mood and immune function. As an essential amino acid, it is not synthesized by the body