D-phenylalanine is a non-protein amino acid related to the essential amino acid l-phenylalanine. d- and

l-phenylalanine are structural mirror images of each other. a small amount of d-phenylalanine may be

converted to l-phenylalanine in the body. d-phenylalanine is reported to inhibit an enzyme that

degrades enkephalins, which are naturally occurring substances in the body that

belong to the class of compounds known as endorphins.