Phenylalanine is an essential amino acid.

Provided by diet, phenylalanine can be converted into another amino acid, tyrosine, in the body. Tyrosine is used to synthesize two key neurotransmitters that promote alertness: dopamine and norepinephrine. 

Phenylalanine  has 3 forms:

• D-phenylalanine;
• L-phenylalanine - most common, the form in which phenylalanine is incorporated into the body’s proteins;
• DL-phenylalanine.