Phenylalanine is an amino acid found in many foods and used by your body to produce proteins and other important molecules.

It has been studied for its effects on depression, pain and skin disorders.

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

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Phenylalanine is an amino acid, which are the building blocks of proteins in your body.

This molecule exists in two forms or arrangements: L-phenylalanine and D-phenylalanine. They’re nearly identical but have a slightly different molecular structure (1).

The L-form is found in foods and used to produce proteins in your body, while the D-form can be synthesized for use in certain medical applications (2, 3).

Your body is unable to produce enough L-phenylalanine on its own, so it’s considered an essential amino acid that must be obtained through your diet (4).

It’s found in a wide variety of foods — both plant and animal sources (5).

In addition to its role in protein production, phenylalanine is used to make other important molecules in your body, several of which send signals between different parts of your body (6).

Phenylalanine has been studied as a treatment for several medical conditions, including skin disorders, depression and pain (3).

However, it can be dangerous for people with the genetic disorder phenylketonuria (PKU) (7).

Summary Phenylalanine is an essential amino acid that is used to produce proteins and signaling molecules. It has been studied as a treatment for several medical conditions but is dangerous for those with a specific genetic disorder.

Your body needs phenylalanine and other amino acids to make proteins.

Many important proteins are found in your brain, blood, muscles, internal organs and virtually everywhere else in your body.

What’s more, phenylalanine is crucial for the production of other molecules, including (3):

  • Tyrosine: This amino acid is produced directly from phenylalanine. It can be used to make new proteins or converted into other molecules on this list (8, 9).
  • Epinephrine and norepinephrine: When you encounter stress, these molecules are vital for your body’s “fight or flight” response (10).
  • Dopamine: This molecule is involved in feelings of pleasure in your brain, as well as forming memories and learning skills (6).

Problems with the normal functions of these molecules may cause negative health effects (9, 11).

Since phenylalanine is used to make these molecules in your body, it has been studied as a potential treatment for certain conditions, including depression (9).

Summary Phenylalanine can be converted to the amino acid tyrosine, which is then used to produce important signaling molecules. These molecules are involved in aspects of your body’s normal functioning, including your mood and stress responses.

Several studies have examined whether phenylalanine may be beneficial in treating particular medical conditions.

Some research has indicated that it may be effective in treating vitiligo, a skin disorder that causes loss of skin color and blotching (12).

Other studies have reported that adding phenylalanine supplements to ultraviolet (UV) light exposure may improve skin pigmentation in individuals with this condition (13, 14).

Phenylalanine can be used to produce the molecule dopamine. Dopamine malfunction in the brain is associated with some forms of depression (6, 15).

One small 12-person study showed a possible benefit of a mixture of the D- and L-forms of this amino acid for treating depression, with 2/3 of patients showing improvement (16).

However, there is minimal other support for phenylalanine’s effects on depression, and most studies have not found clear benefits (17, 18, 19).

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

  • Pain: The D-form of phenylalanine may contribute to pain relief in some instances, though study results are mixed (2, 20, 21, 22).
  • Alcohol withdrawal: A small amount of research indicates that this amino acid, along with other amino acids, may help alleviate symptoms of alcohol withdrawal (23).
  • Parkinson’s disease: Very limited evidence suggests that phenylalanine may be beneficial in treating Parkinson’s disease, but more studies are needed (24).
  • ADHD: Currently, research does not indicate benefits of this amino acid for the treatment of attention deficit hyperactivity disorder (ADHD) (25, 26).
Summary Phenylalanine may be useful in treating the skin disorder vitiligo. Evidence does not provide strong support for the effectiveness of this amino acid in treating other conditions, though limited high-quality research has been conducted.

Phenylalanine is found in many protein-containing foods and is “generally recognized as safe” by the Food and Drug Administration (FDA) (27).

The amount of this amino acid found in foods should not pose a risk for otherwise healthy individuals.

What’s more, few or no side effects are generally observed at supplement doses of 23–45 mg per pound (50–100 mg per kg) of body weight (9, 13).

However, it may be best for pregnant women to avoid taking phenylalanine supplements.

Additionally, there is a very notable exception to the general safety of this amino acid.

Individuals with the amino acid metabolism disorder phenylketonuria (PKU) are unable to process phenylalanine properly. They may have concentrations of phenylalanine in their blood roughly 400 times higher than those without PKU (3, 7).

These dangerously high concentrations can cause brain damage and intellectual disability, as well as problems with the transport of other amino acids to the brain (7, 28).

Due to the seriousness of this disorder, babies are generally screened for PKU soon after birth.

Individuals with PKU are placed on a special low-protein diet, which is generally maintained for life (7).

Summary Phenylalanine is considered safe in the quantities found in normal foods. However, individuals with the disorder phenylketonuria (PKU) cannot metabolize this amino acid and must minimize consumption due to serious health consequences.

Many foods contain phenylalanine, including both plant and animal products.

Soy products are some of the best plant sources of this amino acid, as well as certain seeds and nuts, including soybeans, pumpkin seeds and squash seeds (5).

Soy protein supplements can provide about 2.5 grams of phenylalanine per 200-calorie serving (5, 29).

For animal products, eggs, seafood and certain meats are good sources, providing up to 2–3 grams per 200-calorie serving (5, 29).

Overall, you probably don’t need to specifically select foods based on high phenylalanine content.

Eating a variety of protein-rich foods throughout the day will provide you with all the phenylalanine you need, along with other essential amino acids.

Summary Many foods, including soy products, eggs, seafood and meats, contain phenylalanine. Eating a variety of protein-rich foods throughout the day will provide you with all the amino acids your body needs, including phenylalanine.

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

It may have benefits for the skin disorder vitiligo, but research on its effects on depression, pain or other conditions is limited.

It’s generally considered safe, but people with phenylketonuria (PKU) may experience dangerous side effects.