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Benefits, side effects, and food sources

Phenylalanine is an amino acid that your body uses to make important molecules. This article reviews phenylalanine benefits, side effects, and sources.

This article is based on scientific evidence, written by experts, and fact-checked by experts.
We look at both sides of the argument and strive to be objective, unbiased, and honest.
Phenylalanine: Benefits, side effects, and food sources
Last updated on October 25, 2023, and last reviewed by an expert on March 13, 2023.

Phenylalanine is an amino acid found in many foods.

Phenylalanine: Benefits, side effects, and food sources

It exists in two forms — L-phenylalanine and D-phenylalanine. They’re nearly identical but have slightly different molecular structures.

Because your body cannot produce enough L-phenylalanine alone, it’s an essential amino acid, meaning you must get it from your diet. Good sources include high-protein foods like eggs, dairy, meat, and soy products.

Your body uses L-phenylalanine to make proteins and other important molecules. It has also been studied as a treatment for several medical conditions, including skin disorders and depression.

However, it can be dangerous for people with the genetic disorder phenylketonuria (PKU), which impairs the body’s ability to metabolize phenylalanine.

This article explains all you need to know about phenylalanine, including its benefits, side effects, and food sources.

In this article

Phenylalanine is important for many bodily functions

Your body needs phenylalanine and other amino acids to make proteins found in your brain, blood, muscles, internal organs, and virtually everywhere else in your body.

Phenylalanine is also crucial for the production of other molecules, including:

The dysfunction of these molecules can cause negative health effects, such as depression.

Since your body uses phenylalanine to make these molecules, it has been studied for its link to major depressive disorders.

Summary: Your body can convert phenylalanine into the amino acid tyrosine, which is then used to produce other important molecules. These molecules are involved in several health aspects, including mood, brain function, and stress responses.

Benefits of phenylalanine

Several studies have examined how phenylalanine might benefit the treatment of certain medical conditions.

Tyrosine: Benefits, side effects and dosage
Suggested read: Tyrosine: Benefits, side effects and dosage

Some research indicates that taking phenylalanine supplements alongside ultraviolet (UV) light treatment may improve skin pigmentation in individuals with vitiligo, a skin condition that causes loss of skin pigment.

Phenylalanine can also produce dopamine, which is key to mental health and depression.

In a small, older study from 1977 including 12 people with depression, two-thirds of the participants experienced improved symptoms after taking a mixture of the D- and L-forms of the amino acid.

Newer studies have found low phenylalanine levels could be linked to major depressive disorder.

On the other hand, other older research shows no clear benefits. Ultimately, because there’s limited recent research available on the effects of phenylalanine on depression, more high-quality studies are needed.

In addition to vitiligo and depression, phenylalanine has been studied for potential effects on:

Summary: Phenylalanine may improve the skin disorder vitiligo when combined with UV treatment. At this time, studies do not support the use of this amino acid to treat other conditions.

Dangers and side effects of phenylalanine

Phenylalanine is found in many protein-containing foods and is generally considered safe by the Food and Drug Administration (FDA).

Suggested read: Lactose-free diet: Foods to eat and avoid

The amount found naturally in foods likely doesn’t pose a risk for healthy individuals. Moreover, few or no side effects are generally observed at supplement doses up to 12 grams daily.

Nevertheless, it’s best to use phenylalanine only as directed and check with your doctor before adding any supplements to your routine.

People taking medications for schizophrenia should avoid using phenylalanine, as it could worsen symptoms of tardive dyskinesia, a condition characterized by involuntary, repetitive movements.

Those who are pregnant or breastfeeding should also avoid taking phenylalanine supplements, as there’s limited research on their safety and potential long-term effects.

Furthermore, those with phenylketonuria (PKU) should carefully monitor their amino acid intake. This disorder impairs the body’s ability to metabolize phenylalanine, leading to high blood levels.

Dangerously high blood concentrations of phenylalanine can cause severe brain damage, delayed growth, intellectual disability, and problems transporting other amino acids to the brain.

PKU is also associated with several other disorders, including epilepsy, overactive reflexes, and neurological issues like tics or tremors. Due to the seriousness of this disorder, newborns are generally screened for it soon after birth.

Individuals with PKU are placed on a special low-protein diet to limit their intake of phenylalanine, which is generally maintained for life.

Summary: For healthy adults, phenylalanine is considered safe in the quantities found naturally in foods. However, individuals with phenylketonuria (PKU) cannot metabolize it and must minimize their intake to prevent adverse health effects.

Foods high in phenylalanine

Many high-protein plant and animal foods contain phenylalanine, including meat, fish, poultry, and legumes.

Suggested read: Vegetarian keto diet plan: Benefits, risks, food lists, and more

It’s also found in aspartame, an artificial sweetener often added to diet soda and many sugar-free foods.

Here are some of the top food sources of phenylalanine:

Generally, you don’t need to select foods based on their phenylalanine content. Instead, eating various protein-rich foods throughout the day will provide you with all the phenylalanine you need and other essential amino acids and nutrients.

Summary: Many foods contain phenylalanine, including soy products, eggs, seafood, and meats. Eating various protein-rich foods throughout the day will provide the amino acids your body needs, including phenylalanine.


Phenylalanine is an essential amino acid found in both plant and animal foods.

It may benefit the skin disorder vitiligo, but research on its effects on depression, pain, and other conditions is limited.

While it’s generally considered safe for healthy individuals, it’s important that those with phenylketonuria (PKU) keep their intake low to avoid potentially dangerous side effects.

Talk with your doctor if you notice any negative side effects after taking a phenylalanine supplement or eating high-protein foods.

They can test your amino acid blood levels and help determine your best treatment.

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