Medically reviewed by Aviv Joshua, MS, RDN Phenylalanine is an essential amino acid (building block of protein) that the body doesn't produce, meaning it must be obtained through food. It is found in ...

This supplement is a combination of two types of the phenylalanine amino acid: D-phenylalanine and L-phenylalanine. D-phenylalanine is believed to increase endorphin levels, which serve as our ...

During that same year, Marshall Nirenberg and Heinrich Matthaei began deciphering the genetic code, and they determined that the codon UUU specifically represented the amino acid phenylalanine.