From the Manufacturer:
"Essential amino acid combo promotes healthy mood!
Supports mental clarity and alertness. How Does NSI DL-Phenylalanine Work?
DL-phenylalanine contains the amino acids L-phenylalanine and D-phenylalanine. L-phenylalanine, found naturally in protein-rich foods such as beef, poultry, pork, milk, eggs, and soy, is converted by the body into another amino acid, L-tyrosine. L-tyrosine is responsible for the creation of certain proteins, thyroid hormones, and brain chemicals including dopamine, epinephrine, and norepinephrine. Low levels of these neurotransmitters have been associated with poor mood. Phenylalanine deficiency may also produce feelings of confusion, decreased energy, decreased alertness, and decreased memory."