Phenylalanine comes in several forms as a supplement:
L-phenylalanine is an essential amino acid. It's also found in protein in the foods we eat.
DL-phenylalanine, which contains both the D- and L-forms
Tell your doctor about any supplements you're taking, even if they're natural. That way, your doctor can check on any potential side effects or interactions with any medications.
The U.S. Food and Drug Administration (FDA) does regulate dietary supplements; however, it treats them like foods rather than medications. Unlike drug manufacturers, the makers of supplements don’t have to show their products are safe or effective before selling them on the market.