Phenylalanine is an amino acid. There are three forms: L-, D-, and DL- phenylalanine. L-phenylalanine is found naturally in foods such as meat and eggs.

Amino acids are the building blocks of protein. L-phenylalanine is an essential amino acid. It is the only form of phenylalanine found in proteins. D-phenylalanine is not an essential amino acid, and its role in the body is not currently understood. DL-phenylalanine is made in a lab.

People use phenylalanine for a disorder that causes white patches to develop on the skin (vitiligo). It is also used for attention-deficit hyperactivity disorder (ADHD), chronic pain, aging skin, depression, and many other purposes, but there is no good scientific evidence to support most of these uses.
When taken by mouth: L-phenylalanine is commonly consumed in foods. L-phenylalanine, D-phenylalanine, and DL-phenylalanine are possibly safe when used as medicine, short-term. Side effects might include anxiety, headache, and constipation.

When applied to the skin: Phenylalanine cream is possibly safe when used short-term.

Special Precautions & Warnings:

Pregnancy: L-phenylalanine is commonly consumed in foods. But having too much phenylalanine during pregnancy can increase the chance of birth defects. For patients who process phenylalanine normally and have normal levels, it is fine to consume phenylalanine in typical food amounts, but supplements containing phenylalanine should be avoided. For pregnant patients who have high levels of phenylalanine, such as those with a condition called phenylketonuria (PKU), even normal food amounts are unsafe. For these patients, experts recommend a low phenylalanine diet for at least 20 weeks before getting pregnant. This should reduce the risk of birth defects.

Breast-feeding: L-phenylalanine is commonly consumed in foods. But there isn't enough reliable information to know if any form of phenylalanine is safe to use in larger amounts as medicine while breast-feeding. Stay on the safe side and avoid use.

Phenylketonuria (PKU) and other conditions that cause high levels of phenylalanine: Some people have inherited disorders, such as PKU, that cause their bodies to build up too much phenylalanine. This can cause developmental delay, high blood pressure, stroke, and many other serious health issues. If you have one of these disorders, avoid phenylalanine supplements.

Schizophrenia: Some people with schizophrenia have a movement disorder called tardive dyskinesia. Phenylalanine might make this movement disorder worse.


NatMed Pro rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.
Likely effective Effectiveness definitions
Possibly effective Effectiveness definitions
  • A skin disorder that causes white patches to develop on the skin (vitiligo). Taking L-phenylalanine by mouth, or applying it to the skin, both in combination with UVA light, seems to improve symptoms of vitiligo.
Likely ineffective Effectiveness definitions
Possibly ineffective Effectiveness definitions
  • Attention deficit-hyperactivity disorder (ADHD). Taking phenylalanine by mouth doesn't seem to help ADHD.
  • Chronic pain. Taking D-phenylalanine by mouth does not seem to reduce pain.
There is interest in using phenylalanine for a number of other purposes, but there isn't enough reliable information to say whether it might be helpful.
Insufficient evidence Effectiveness definitions

Dosing & administration

L-phenylalanine is an essential amino acid found in foods including meat, fish, eggs, cheese, and milk.

As medicine, L-phenylalanine, D-phenylalanine, and DL-phenylalanine have been used in varying doses. L-phenylalanine has most often been used by adults in doses of 250 mg or 100 mg/kg by mouth daily for up to 3 months. Speak with a healthcare provider to find out what form and dose might be best for a specific condition.

Interactions with pharmaceuticals


Interaction Rating=Moderate Be cautious with this combination.

Phenylalanine might decrease how much baclofen the body absorbs. This might decrease the effects of baclofen.


Interaction Rating=Major Do not take this combination.

Levodopa is used for Parkinson disease. Taking phenylalanine along with levodopa can make Parkinson disease worse. Do not take phenylalanine if you are taking levodopa.

Medications for depression (MAOIs)

Interaction Rating=Moderate Be cautious with this combination.

Phenylalanine can increase a chemical in the body called tyramine. Large amounts of tyramine can cause high blood pressure. Some medications used for depression stop the body from breaking down tyramine. This can cause there to be too much tyramine and lead to dangerously high blood pressure.

Some common MAOIs include phenelzine (Nardil), selegiline (Zelapar), and tranylcypromine (Parnate).

Interactions with herbs & supplements

There are no known interactions with herbs and supplements.

Interactions with foods

There are no known interactions with foods.
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