Science-Based Nutrition Dietary Supplement 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."* Suitable for Vegetarians Questions? 777-2474 *These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.