DL-Phenylalanine is a combination of the well-tolerated essential amino acids, d-phenylalanine and l-phenylalanine. Together, these compounds help promote mental functioning and support positive outlook. l-Phenylalanine is a precursor to l-tyrosine, which converts to the neurotransmitters norepinephrine, epinephrine, dopamine and tyramine. l-Tyrosine and its metabolites may support emotional well-being, memory and learning. d-Phenylalanine may promote the levels of certain endorphins, thereby calming stressed muscles and joints.