L-tryptophan is an essential amino acid precursor to serotonin, a critical neurotransmitter, which is key for stabilizing mood, relieving panic and anxiety, and maintaining a normal sleep-wake pattern. Tryptophan is a precursor for the B vitamin, niacin, which is important for normal digestion, skin, nerves, as well as serotonin. Tryptophan in the form of l-tryptophan is considered 100% digestible and available to the animal.