DL-Phenylalanine is the combined left and right isomers of the essential amino acid, phenylalanine. Phenylalanine is an amino acid, a component of proteins which is also used by the body to build neurotransmitters, chemicals which conduct electrical impulses in the brain and nervous system. L-phenylalanine, the left handed molecule, is converted to L-tyrosine, then L-dopa, then norepinephrine, the brain's primary upper or feel-good neurotransmitter. D-Phenylalanine, the right handed version is converted primarily to phenylethylamine, made famous as the "feeling in love" chemical found in chocolate (though in very small quantities there.)

DL-phenylalanine refers to a racemic mixture consisting of 50% D-phenylalanine and 50% L-phenylalanine. L-phenylalanine is an essential protein amino acid. (See L-Phenylalanine.) D-phenylalanine is the enantiomer of L-phenylalanine. D-phenylalanine is a nonprotein amino acid, meaning that it does not participate in protein biosynthesis. D-phenylalanine and other D-amino acids are, however, found in proteins, in small amounts, particularly aged proteins and food proteins that have been processed. The biological functions of D-amino acids remain unclear. Some D-amino acids, such as D-phenylalanine, may have pharmacologic activity.

The putative analgesic activity of DL-phenylalanine may be explained by the possible blockage by D-phenylalanine of enkephalin degradation by the enzyme carboxypeptidase A. The mechanism of DL-phenylalanine's putative antidepressant activity may be accounted for by the precursor role of L-phenylalanine in the synthesis of the neurotransmitters norepinephrine and dopamine. Elevated brain norepinephrine and dopamine levels are thought to be associated with antidepressant effects.

DL-Phenylalanine is a combination of the well-tolerated essential amino acids, d- phenylalanine and l-phenylalanine. Together, these compounds promote mental functioning, support a positive outlook, and relax the musculoskeletal system. l- Phenylalanine is a precursor to tyrosine, which converts to the neurotransmitters norepinephrine, epinephrine, dopamine and tyramine. Tyrosine and its metabolites have been shown to support emotional well-being, memory and learning. d-Phenylalanine may regulate the levels of certain endorphins, thereby calming stressed muscles and joints. By maintaining healthy tyrosine and endorphin levels, dl-phenylalanine nutritionally supports mental acuity and emotional well-being, while relaxing stressed muscles and joints.

Phenylalanine is an essential amino acid found in common protein foods as well as the synthetic sweetener aspartame (NutraSweet). Like other nutrient amino acids, phenylalanine comes in L- (from the Latin levo for left) and D- (from dextro for right) forms. The directions refer to minor differences in the amino acids' molecular structure, as evidenced by light refraction. L-phenylalanine is predominantly a nervous system stimulant, mood enhancer, and appetite suppressant. While D-phenylalanine also apparently has antidepressant properties, it is taken primarily to control chronic pain. Synthetic DL-phenylalanine (DLPA) is half L-phenylalanine and half D-phenylalanine. DLPA has some of the effects of both forms of phenylalanine, although most people take it for the pain-relieving effects of D-phenylalanine.