Phenylalanine is an amino acid found in many foods.
It exists in two forms — L-phenylalanine and D-phenylalanine. They’re nearly identical but have slightly different molecular structures (1, 2).
Because your body is unable to produce enough L-phenylalanine on its own, it’s considered an essential amino acid, meaning you need to 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 (2).
However, it can be dangerous for people with the genetic disorder phenylketonuria (PKU), which impairs the body’s ability to metabolize phenylalanine (5).
This article explains all you need to know about phenylalanine, including its benefits, side effects, and food sources.
Your body needs phenylalanine and other amino acids to make proteins, which are 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 (2):
- Tyrosine. This amino acid is produced directly from phenylalanine. Your body uses it to make new proteins or converts it into other molecules like epinephrine (6).
- Epinephrine and norepinephrine. When you experience stressful situations, these molecules are vital to your body’s fight or flight response (
- Dopamine. This neurotransmitter is an important part of your brain’s reward center and involved in motor control, memory, and learning (
The dysfunction of these molecules can cause negative health effects, such as depression (
In fact, since your body uses phenylalanine to make these molecules, it has been studied for its link to major depressive disorders (
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 aspects of health, including your mood, brain function, and stress responses.
Several studies have examined how phenylalanine might benefit the treatment of certain medical conditions.
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 be used to produce dopamine, a molecule that plays a key role in mental health and depression (2,
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 (16).
Newer studies have similarly found that low levels of phenylalanine 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:
- Pain. Some older studies have found that D-phenylalanine might relieve pain, but overall, research has turned up mixed results (1,
20, 21, 22).
- Alcohol withdrawal. According to a 2011 study, using a supplement that contained D-phenylalanine along with other amino acids could help alleviate symptoms of alcohol withdrawal (
- Parkinson’s disease. An older study suggests that phenylalanine may support Parkinson’s disease treatment, but more research is needed. Although inconclusive, tyrosine has also been studied for its effects on brain function and Parkinson’s (
24, 25, 26).
- ADHD. Currently, research does not indicate that this amino acid has any benefits for the treatment of attention deficit hyperactivity disorder (ADHD) (
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.
Phenylalanine is found in many protein-containing foods and considered to be generally recognized as safe by the Food and Drug Administration (FDA) (28).
The amount found naturally in foods likely doesn’t pose a risk for healthy individuals. What’s more, few or no side effects are generally observed at supplement doses up to 12 grams per day (2,
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 monitor their intake of the amino acid carefully. This disorder impairs the body’s ability to metabolize phenylalanine, which can lead to high levels in the blood (
Dangerously high blood concentrations of phenylalanine can cause severe brain damage, delayed growth, intellectual disability, and problems with the transport of other amino acids to the brain (5,
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 (5).
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.
Many high protein plant and animal foods contain phenylalanine, including meat, fish, poultry, and legumes.
It’s also found in aspartame, an artificial sweetener that’s often added to diet soda and many sugar-free foods (
Here are some of the top food sources of phenylalanine (
- Meat: beef, pork, lamb, venison
- Poultry: chicken, turkey, duck, goose
- Seafood: salmon, trout, tuna, mackerel, shrimp, lobster
- Eggs: whole eggs, egg whites
- Dairy: milk, cheese, yogurt
- Nuts: almonds, pistachios, macadamia nuts, cashews, walnuts
- Seeds: pumpkin seeds, squash seeds, hemp seeds, sunflower seeds
- Nut butters: peanut butter, almond butter, cashew butter
- Legumes: lentils, chickpeas, black beans, kidney beans
- Whole grains: quinoa, oats, rye, barley, wheat
- Soy products: soybeans, tofu, tempeh, edamame, protein supplements
- Diet products: diet soda and sugar-free ice cream, gum, candies, and flavored yogurts made with aspartame
Generally, you don’t need to select foods based on their phenylalanine content. Instead, 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 and nutrients.
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 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.
If you notice any negative side effects after taking a phenylalanine supplement or eating high protein foods, talk with your doctor.
They can test your amino acid blood levels and help determine the best course of treatment for you.
Just one thing
Try this today: There are plenty of simple and delicious ways to ramp up your intake of protein and ensure that you’re getting enough phenylalanine. Check out this article for 20 tasty high protein foods that are easy to add to your diet.