Established 1971 May Support Comfort Essential Amino Acid Precursor to Brain Neurotransmitters Dietary Supplement Our Pledge of Integrity Authenticity Cleanliness Freshness Consistency Accuracy DL-Phenylalanine (DLPA) is 50% D and 50% L forms of the amino acid phenylalnine. D-phenylalanine is an enkephalinase inhibitor and may help to block the degradation of enkephalins which may support comfort. L-phenylalanine is a precursor to the neurotransmitters in the brain.