The Health Benefits of Phenylalanine

Researchers continue to investigate the potential uses

Phenylalanine is an aromatic amino acid that is present in three different compounds: L-phenylalanine, D-phenylalanine, and DL-phenylalanine.

L-phenylalanine is an essential amino acid—the body produces it but doesn't make the full amount it needs, so it must be received through foods. D-phenylalanine is a synthesized form and is used as a supplement. DL-phenylalanine is a mixture of L and D phenylalanine—it is also created in a lab and used as a supplement.

While phenylalanine has been studied for use in treating some conditions, there isn't currently a lot of evidence to support its use. Research is still being done—scientists think there might be reasons to continue looking at its effectiveness. It is generally thought to be safe for most healthy people, but it can be expensive, so it is often not thought of as a priority treatment if a patient is already using other medications.

Health Benefits

Phenylalanine supplements have been studied for use in pain relief as well as to treat various health conditions including attention deficit-hyperactivity disorder (ADHD), depression, Parkinson's disease, multiple sclerosis, and vitiligo.

Phenylalanine has not been studied for use in treating osteoarthritis or rheumatoid arthritis, so there is currently no scientific basis for recommending it to treat these conditions.

The following are conditions that phenylalanine has been tested in treating. While most of the results are inconclusive, pending further studies, researchers find that there may be reason to continue investigating its use.

ADHD

Phenylalanine supplements have been studied to treat ADHD, a condition usually diagnosed in children and associated with being impulsive and having difficulty maintaining attention. Studies were done to see if there was a lack of amino acids in kids diagnosed with ADHD, which would then suggest that supplementing with phenylalanine could treat symptoms.

A few small studies showed that children with ADHD showed a lower level of certain aromatic amino acids (such as phenylalanine) in their blood. However, a larger study of other kids with ADHD showed no lack of these amino acids in their blood. Studies done on adults with ADHD in the 1980s and 90s failed to show any benefit from supplementing with amino acids that lasting beyond three months.

The general consensus is that phenylalanine is not a proven treatment for ADHD.

Pain Relief

Some studies were done to see if supplementing with phenylalanine helped increase or extend the effect of certain painkillers or of the analgesic use of acupuncture. It was thought that because phenylalanine and other amino acids are involved in the creation of chemical messengers in the body that help suppress pain, that supplementing might increase the effect of painkillers.

Most of the studies were small and the results were mainly mixed. At this point, without larger studies in this area, there’s not enough evidence to recommend supplementing with phenylalanine for use in pain relief or as a way to increase the pain relief effect from opioids or acupuncture.

Depression

Phenylalanine is used by the body in the process of creating a neurotransmitter called dopamine. A lack of dopamine may be associated with some forms of depression. Therefore, it is thought that supplementing with phenylalanine could help treat the symptoms of depression in cases where it is thought to be the result of a problem with dopamine production.

In one study, participants who were recovered from depression were split into two groups and after fasting, one group was given a drink containing amino acids (including phenylalanine) and one was given a drink that didn’t contain any amino acids. Those who didn’t receive the amino acids didn’t appear to have any difference in mood from those who did receive them.

A few small, older studies showed that supplementing with phenylalanine had an effect on depressed mood for some patients. Another study showed that people who received DL-phenylalanine were more optimistic than those who did not.

Given that many studies were small and some had conflicting results, there’s currently not enough evidence to recommend the use of phenylalanine as a treatment for depression or other mood disorders.

Alcohol Withdrawal Symptoms

One small study looked at the effect of adding a supplement of D-phenylalanine, L-glutamine, and L-5-hydroxytryptophan to the diet of patients going through an alcohol detoxification program. At the end of the 40-day study, researchers did note that those receiving the supplement saw benefits, saying that the supplement "alleviates the withdrawal symptoms.” 

However, the study did not look at phenylalanine alone—it was given as part of a combination, so it’s not clear what role phenylalanine plays by itself. More studies are needed in order to understand if phenylalanine could be used as a treatment during alcohol detox, so it's not recommended for use in this area right now.

Parkinson’s Disease

Some studies have shown that people with Parkinson’s disease have higher amounts of phenylalanine in their blood. Phenylalanine is used by the body to make another amino acid called tyrosine. People with Parkinson’s disease have also been shown to have lower amounts of tyrosine in their bodies than those who don’t have the disease.

The high phenylalanine and low tyrosine seem to mean that there’s a disconnect in the conversion process. Currently, however, it’s not thought that phenylalanine supplements have any benefit for people with Parkinson’s disease or other types of movement disorders.

Phenylalanine supplements can actually make one of the treatments for Parkinson’s disease, levodopa (Dopar, Larodopa), less effective.

People taking levodopa shouldn’t also take phenylalanine supplements.

Multiple Sclerosis

Two studies looking into supplementing with lofepramine, L-phenylalanine, and intramuscular vitamin B-12 for multiple sclerosis showed some improvements for patients in certain clinical areas. Another study used a TENS (transcutaneous electrical nerve stimulation) unit in combination with a phenylalanine supplement.

The studies done so far are experimental, so there are no current recommendations to start using phenylalanine to treat multiple sclerosis because it’s not clear that there would be any real benefit.

In addition, phenylalanine was not used alone in the studies, so there is no evidence that supplementing with this amino acid by itself would have any effect.

Vitiligo

Vitiligo is an unpredictable condition that causes the loss of pigment in the skin, which results in the appearance of white patches. Some studies have shown that phenylalanine, when in combination with other substances and with the use of UV light, may be helpful in treating vitiligo. There has also been a study on the use of 10 percent L-phenylalanine cream, which is put on the skin twice a day either alone or also with the use of phototherapy.

The topical creams containing L-phenylalanine were shown to be effective in treating vitiligo, especially when combined with phototherapy.

Topical phenylalanine may be recommended in certain cases, but more solid evidence is needed before this treatment is recommended for more widespread use.

Possible Side Effects

For most people, phenylalanine supplements in recommended amounts are considered to be safe. However, for certain groups of people it is not recommended.

People Who Should Not Take Phenylalanine

  • Pregnant women
  • Women who are breastfeeding their babies
  • Women who want to become pregnant
  • People with the condition phenylketonuria (PKU)
  • People with schizophrenia

Phenylalanine is not recommended for pregnant women, those who are breastfeeding (effects of phenylalanine on nursing infants is unknown), and women who want to become pregnant who already show higher than normal amounts of phenylalanine in their blood. Consult a doctor first.

For people who have a rare, inherited condition called phenylketonuria (PKU), phenylalanine can be dangerous. People with PKU have a lack of or a total absence of the enzyme phenylalanine hydroxylase, which breaks down phenylalanine.

Without this enzyme, phenylalanine builds up in the blood and leads to brain damage. Since this condition can cause damage so rapidly, babies are tested for PKU at birth. Throughout their lives, people with PKU must avoid foods containing phenylalanine and should not take phenylalanine supplements.

For people who are diagnosed with schizophrenia, supplementing with phenylalanine could increase the risk of worsening an associated movement disorder called tardive dyskinesia. People taking levodopa should not take a phenylalanine supplement.

Dosage and Preparation

For most of the conditions described above, there is no scientific evidence to support the use of phenylalanine as a treatment. It’s important to discuss the use of any supplement with a physician, including phenylalanine.

Phenylalanine is thought to be safe for most people, but there are some cases where it can be dangerous—in other cases, there’s no proof that it will work for the condition for which it is being taken. 

One condition for which phenylalanine has been studied and may be recommended by physicians as a treatment is the skin condition vitiligo.

For vitiligo, L-phenylalanine has been studied for use for three or four months. Phenylalanine for vitiligo has been studied is recommended for adults as an oral medication (50 to 100 milligram/kilogram of L-phenylalanine per day or 50 mg/kg up to three times a week). As a topical medication, a cream containing 10 percent phenylalanine can be applied twice per day

For children, the oral medication dose is 100 mg/kg of L-phenylalanine taken twice a week.

What to Look For

Phenylalanine supplements are not regulated by the Food and Drug Administration (FDA). Any supplement packaging should claim, "These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.”

For those in whom a phenylalanine supplement is recommended, checking with a doctor about the brand and/or type to use is the best course of action. All supplements of phenylalanine (L-phenylalanine, D-phenylalanine, and DL-phenylalanine) are made in a laboratory. 

Phenylalanine is found naturally in many foods. Some of the foods that have higher concentrations of phenylalanine include eggs, soy, cod, tofu, and parmesan cheese.

Other Questions

Is it necessary to take a phenylalanine supplement outside of your diet in order to make sure I am receiving enough?

Most people will get enough phenylalanine in their diet by eating a wide variety of foods.

A Word From Verywell

There’s little to no evidence for using phenylalanine to treat any condition other than vitiligo. In some cases, it’s been shown to be ineffective and in others, there’s not enough evidence to determine if it would be helpful or not. Phenylalanine is safe for most people except in certain cases (such as those who have PKU), but it could be harmful if people stop taking proven medication in order to take phenylalanine to treat a particular condition. Check with a physician before deciding to supplement with phenylalanine. 

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