Equip yourself. Learn about phenylalanine.


Phenylalanine is an amino acid, and in particular one of the twenty common amino acids, which are used to form proteins. It is classified as an essential amino acid. In addition to natural phenylalanine, there are also forms which are synthesized in a laboratory: the D and DL types.

Phenylalanine supplements

Often sold as a nutritional or dietary supplement, phenylalanine claims include effects such as painkiller (analgesic) and antidepressant. Furthermore, it is a direct precursor to another nutritional supplement, phenylethylamine.

This amino acid is also able to be converted into L-tyrosine, from there into L-DOPA, and once again into dopamine and a few catecholamines: adrenaline, noradrenaline, and dopamine. Moreover, together with tyrosine, phenylalanine can form lignan.

Read additional information on supplements.


Phenylalanine deficiency is a legitimate health issue in some individuals. When the body does not have sufficient levels of this amino acid, some symptoms which may appear include:

Lack of energy
Loss or reduction of appetite
Memory worsening
Reduced alertness

Continue reading about deficiency.


The genetic disorder in which there is an phenylalanine metabolism inability is known as phenylkentonuria (PKU); sufferers of this condition are phenylketonurics. Since their bodies do not properly metabolize it, individuals with PKU should avoid ingesting sizeable amounts.

In the United States, Canada, and Australia, products containing the aspartame artificial sweetener are required to carry the label: "Phenylketonurics: Contains phenylalanine." Other countries may have other requirements, such as in the United Kingdom where such products must mention aspartame or E951 (E number additive code) in their ingredient panels, and have a label stating "Contains a source of phenylalanine."

Phenylketonuria generally begins displaying symptoms in patients age 3 to 6 months. Some potential symptoms of PKU include:

Delays in development
Small head (abnormal)

Read more on phenylketonuria.


Some pregnant women also have a condition known as hyperphenylalanine, in which the blood contains high levels of this particular amino acid due to improper metabolism of it. They too should avoid dietary intake of it.