What Is Phenylalanine?
Phenylalanine is an essential amino acid. Among the 20 amino acids, nine are essential. Phenylalanine is one of the building blocks of protein. It's one of the nine amino acids your body can't make, so you have to get phenylalanine through your diet or supplements.
Your body needs phenylalanine to make the proteins found throughout your body, such as your muscles, brain, and other organs. Your body also uses phenylalanine to make tyrosine, to make the hormones epinephrine and norepinephrine, as well as the neurotransmitter dopamine. All are important in controlling your mood and stress responses.
Phenylalanine Benefits
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.
- D-phenylalanine
- DL-phenylalanine, which contains both the D- and L-forms
There have been many studies on whether phenylalanine can benefit certain medical conditions, including depression, because of its connection to dopamine. Dopamine controls pleasure, and the inability to experience pleasure is a common symptom of depression.
Some research also suggests that taking phenylalanine, combined with UV light treatment, may be good for treating vitiligo. Because phenylalanine helps make melanin in your body, it may also help restore the pigment in your skin.
Phenylalanine is also commonly used to treat the symptoms of other conditions, such as:
Keep in mind that the quality and active ingredients in supplements may vary widely from maker to maker, which makes it difficult to set standard doses. Talk to your doctor or health care provider before you start taking any supplement.
Phenylalanine Food Sources
Phenylalanine is found in most foods that contain protein, including:
- Meats
- Poultry
- Seafood
- Eggs
- Nuts and seeds, as well as their butters
- Soy products
- Cheese
- Legumes
- Food and drinks containing aspartame
Risks and Side Effects of Phenylalanine
If you're healthy and eat a variety of protein-rich foods, you shouldn't have to worry about how much phenylalanine you consume. The amount of phenylalanine found in food doesn't pose a health risk for most people. Some studies have explored doses of phenylalanine supplements up to 12 grams per day. But this is well above what you'd typically get from your diet, and it's not recommended unless a doctor says it's OK. There's also limited evidence on whether such high doses are safe or effective.
Risks
If you have certain medical conditions, you shouldn't take phenylalanine supplements, including if you're on any medications for schizophrenia. Phenylalanine may worsen the symptoms of tardive dyskinesia, a movement disorder that's linked to antipsychotic medications, such as chlorpromazine (Thorazine), fluphenazine (Prolixin), and haloperidol (Haldol).
Also, the genetic condition phenylketonuria (PKU) causes mutations in both copies of the PAH gene. When you have PKU, the levels of phenylalanine build up in your body. High levels of phenylalanine in your body can damage the brain and cause developmental delays, cognitive problems, and intellectual disabilities. PKU is also linked to other serious neurological disorders, such as epilepsy, limb spasticity, and tremors. Because it's so serious, newborns are screened after birth. Treatment includes a special diet and medication.
If you're breastfeeding or pregnant, you shouldn't take phenylalanine, as there's little research or scientific evidence on whether it's safe.
Interactions
Phenylalanine may affect how your body breaks down other drugs and supplements. 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. FDA does regulate dietary supplements but uses a different set of rules than it does for "conventional" foods or drugs. Unlike drugmakers, the makers of supplements don’t have to show their products are safe or effective before selling them.
Phenylalanine FAQs
Do humans need phenylalanine?
Yes. Phenylalanine is an essential amino acid, which means your body needs it to function properly. But your body can't make it, so you have to get it from the foods you eat.
Why is there a warning label for phenylalanine?
Products such as diet sodas that have artificial sweetener aspartame (Equal, NutraSweet) also contain phenylalanine. In the U.S., products with aspartame must have a warning on the label about phenylalanine, mainly for people who have the genetic condition phenylketonuria (PKU), as they can't process the amino acid. The warning label lets them know not to eat or drink the product with phenylalanine.