Phenylalanine: Potential Benefits + Foods & Side Effects

Phenylalanine: Uses and Risks

Phenylalanine: Potential Benefits + Foods & Side Effects

Phenylalanine comes in several forms as a supplement:

  • L-phenylalanine is an essential amino acid. It's also found in protein in the foods we eat.
  • D-phenylalanine
  • DL-phenylalanine, which contains both the D- and L-forms

Phenylalanine is not a widely accepted treatment for any condition. But people have tried to treat a number of conditions with phenylalanine, including:

  • Chronic pain
  • Depression
  • ADHD
  • Vitiligo (light-colored patches on the skin)

Some research, mainly from the 1970s and 1980s, offers some support for using it for depression. Several studies also showed that L-phenylalanine plus ultraviolet A light may be helpful for people with vitiligo.

There is less evidence to support its use for other conditions.

Optimal doses of phenylalanine have not been set for any condition. Quality and active ingredients in supplements may vary widely from maker to maker. This makes it difficult to set a standard dose. However, commonly used dosages, depending on the condition, range from 150 mg to 5,000 mg daily.

Phenylalanine is found in many foods, including:

  • Meat
  • Eggs
  • Fish
  • Cheese
  • Products containing aspartame

Phenylalanine can trigger allergic reactions, with symptoms such as:

Side effects may include:

Doses higher than 5,000 milligrams a day can cause nerve damage.

Risks. People with certain conditions should avoid using this supplement, including those with Schizophrenia (Tardive dyskinesia, a movement disorder, may develop.) You also should avoid the supplement if you have a sensitivity to phenylalanine or a condition in which your body can't break down phenylalanine.

And use caution in taking phenylalanine if you have:

  • High blood pressure
  • Trouble sleeping
  • Anxiety or other psychiatric problems

Also, it is unknown whether this supplement is safe in women who are pregnant or breastfeeding.

Interactions. Phenylalanine can cause tardive dyskinesia in people taking antipsychotic medicines.

If taken with certain antidepressants, this supplement could lead to:

  • Hypomania
  • Constipation
  • Insomnia
  • Higher blood pressure

Phenylalanine might also:

It may also affect how your body breaks down other drugs and supplements. And use with caution if you are taking a monoamine oxidase inhibitor (MAOI) drug and several other classes of medications; talk to your doctor or pharmacist about this.

Tell your doctor about any supplements you're taking, even if they're natural. That way, your doctor can check on any potential side effects or interactions with any medications.

The U.S. Food and Drug Administration (FDA) does regulate dietary supplements; however, it treats them foods rather than medications. Un drug manufacturers, the makers of supplements don’t have to show their products are safe or effective before selling them on the market.


Natural Standard Professional Monograph: “Phenylalanine.”

AltCareDex, “Phenylalanine.”

American Academy of Dermatology: “Vitiligo.”

March of Dimes: “PKU (Phenylketonuria).”

Natural Standard Bottom Line Monograph: “Phenylalanine.”

University of Maryland Medical Center: “Phenylalanine.”

© 2019 WebMD, LLC. All rights reserved.


Essential amino acids: Definition, benefits, and foods

Phenylalanine: Potential Benefits + Foods & Side Effects

The body needs 20 different amino acids to maintain good health and normal functioning. People must obtain nine of these amino acids, called the essential amino acids, through food. Good dietary sources include meat, eggs, tofu, soy, buckwheat, quinoa, and dairy.

Amino acids are compounds that combine to make proteins. When a person eats a food that contains protein, their digestive system breaks the protein down into amino acids. The body then combines the amino acids in various ways to carry out bodily functions.

A healthy body can manufacture the other 11 amino acids, so these do not usually need to enter the body through the diet.

Amino acids build muscles, cause chemical reactions in the body, transport nutrients, prevent illness, and carry out other functions. Amino acid deficiency can result in decreased immunity, digestive problems, depression, fertility issues, lower mental alertness, slowed growth in children, and many other health issues.

Each of the essential amino acids plays a different role in the body, and the symptoms of deficiency vary accordingly.

There are many types of essential amino acids, including:


Lysine plays a vital role in building muscle, maintaining bone strength, aiding recovery from injury or surgery, and regulating hormones, antibodies, and enzymes. It may also have antiviral effects.

There is not a lot of research available on lysine deficiency, but a study on rats indicates that lysine deficiency can lead to stress-induced anxiety.


Histidine facilitates growth, the creation of blood cells, and tissue repair. It also helps maintain the special protective covering over nerve cells, which is called the myelin sheath.

The body metabolizes histidine into histamine, which is crucial for immunity, reproductive health, and digestion. The results of a study that recruited women with obesity and metabolic syndrome suggest that histidine supplements may lower BMI and insulin resistance.

Deficiency can cause anemia, and low blood levels appear to be more common among people with arthritis and kidney disease.


Threonine is necessary for healthy skin and teeth, as it is a component in tooth enamel, collagen, and elastin. It helps aid fat metabolism and may be beneficial for people with indigestion, anxiety, and mild depression.

A 2018 study found that threonine deficiency in fish led to these animals having a lowered resistance to disease.


Methionine and the nonessential amino acid cysteine play a role in the health and flexibility of skin and hair. Methionine also helps keep nails strong. It aids the proper absorption of selenium and zinc and the removal of heavy metals, such as lead and mercury.


Valine is essential for mental focus, muscle coordination, and emotional calm. People may use valine supplements for muscle growth, tissue repair, and energy.

Deficiency may cause insomnia and reduced mental function.


Isoleucine helps with wound healing, immunity, blood sugar regulation, and hormone production. It is primarily present in muscle tissue and regulates energy levels.

Older adults may be more prone to isoleucine deficiency than younger people. This deficiency may cause muscle wasting and shaking.


Leucine helps regulate blood sugar levels and aids the growth and repair of muscle and bone. It is also necessary for wound healing and the production of growth hormone.

Leucine deficiency can lead to skin rashes, hair loss, and fatigue.


Share on PinterestSome diet sodas contain sweeteners with phenylalanine.

Phenylalanine helps the body use other amino acids as well as proteins and enzymes. The body converts phenylalanine to tyrosine, which is necessary for specific brain functions.

Phenylalanine deficiency, though rare, can lead to poor weight gain in infants. It may also cause eczema, fatigue, and memory problems in adults.

Phenylalanine is often in the artificial sweetener aspartame, which manufacturers use to make diet sodas. Large doses of aspartame can increase the levels of phenylalanine in the brain and may cause anxiety and jitteriness and affect sleep.

People with a rare genetic disorder called phenylketonuria (PKU) are unable to metabolize phenylalanine. As a result, they should avoid consuming foods that contain high levels of this amino acid.


Tryptophan is necessary for proper growth in infants and is a precursor of serotonin and melatonin. Serotonin is a neurotransmitter that regulates appetite, sleep, mood, and pain. Melatonin also regulates sleep.

Tryptophan is a sedative, and it is an ingredient in some sleep aids. One study indicates that tryptophan supplementation can improve mental energy and emotional processing in healthy women.

Tryptophan deficiency can cause a condition called pellagra, which can lead to dementia, skin rashes, and digestive issues.

Many studies show that low levels of protein and essential amino acids affect muscle strength and exercise performance.

According to a 2014 study, not getting enough essential amino acids may cause lower muscle mass in older adults.

An additional study shows that amino acid supplements can help athletes recover after exercise.

Doctors previously believed that people had to eat foods that provided all nine essential amino acids in one meal.

As a result, unless an individual was eating meat, eggs, dairy, tofu, or another food with all the essential amino acids, it was necessary to combine two or more plant foods containing all nine, such as rice and beans.

Today, however, that recommendation is different. People who eat vegetarian or vegan diets can get their essential amino acids from various plant foods throughout the day and do not necessarily have to eat them all together at one meal.

Share on PinterestA person should speak to their doctor before taking essential amino acid supplements.

Although 11 of the amino acids are nonessential, humans may require some of them if they are under stress or have an illness. During these times, the body may not be able to make enough of these amino acids to keep up with the increased demand. These amino acids are “conditional,” which means that a person may require them in certain situations.

People may sometimes wish to take essential amino acid supplements. It is best to seek advice from a doctor first regarding safety and dosage.

Although it is possible to be deficient in essential amino acids, most people can obtain enough of them by eating a diet that includes protein.

The foods in the following list are the most common sources of essential amino acids:

  • Lysine is in meat, eggs, soy, black beans, quinoa, and pumpkin seeds.
  • Meat, fish, poultry, nuts, seeds, and whole grains contain large amounts of histidine.
  • Cottage cheese and wheat germ contain high quantities of threonine.
  • Methionine is in eggs, grains, nuts, and seeds.
  • Valine is in soy, cheese, peanuts, mushrooms, whole grains, and vegetables.
  • Isoleucine is plentiful in meat, fish, poultry, eggs, cheese, lentils, nuts, and seeds.
  • Dairy, soy, beans, and legumes are sources of leucine.
  • Phenylalanine is in dairy, meat, poultry, soy, fish, beans, and nuts.
  • Tryptophan is in most high-protein foods, including wheat germ, cottage cheese, chicken, and turkey.

These are just a few examples of foods that are rich in essential amino acids. All foods that contain protein, whether plant-based or animal-based, will contain at least some of the essential amino acids.

Consuming essential amino acids is crucial for good health.

Eating a variety of foods that contain protein each day is the best way for people to ensure that they are getting adequate amounts of essential amino acids. With today’s modern diet and access to a wide variety of foods, deficiency is rare for people who are generally in good health.

People should always talk to a doctor before using supplements.


Safety Concerns Regarding Supplemental Amino Acids: Results of a Study

Phenylalanine: Potential Benefits + Foods & Side Effects

In the late summer and fall of 1989 there suddenly appeared a number of individuals who developed eosinophilia-myalgia syndrome (EMS) associated with the use of supplemental L-tryptophan (Hertzman et al., 1990; Kamb et al., 1992).

This amino acid, which has been used for many years for its pharmacological properties (e.g., as a sedative-hypnotic, analgesic, and anorexiant), was available to consumers under the guise of a “dietary supplement” in health food stores, pharmacies and grocery or department stores (Young, 1986).

More than 30 individuals died and many thousands were severely injured in the United States alone as a result of exposure to what is now believed to have been a contaminant in one manufacturer's L-tryptophan.

This contaminant, 1,1'-ethylene-bis (tryptophan), commonly referred to as “Peak 97” or “Peak E,” was produced during the manufacture of this amino acid (Mayeno et al., 1990).

A number of other impurities have since been detected in implicated lots of L-tryptophan, the concentrations of which varied significantly over time as the manufacturer presumably modified synthesis and/or purification conditions during its quest to produce this amino acid more efficiently.

Largely as a result of the tragic EMS epidemic that resulted from the use of L-tryptophan, the U.S.

Food and Drug Administration (FDA) contracted with the Life Sciences Research Office (LSRO) of the Federation of the American Societies for Experimental Biology (FASEB) to perform an extensive review of the scientific literature to determine the safety of amino acids used as dietary supplements (Federation of the American Societies for Experimental Biology, Life Sciences Research Office, 1992). Not only was L-tryptophan use to be assessed for safety, but in addition, all the available amino acids were to be evaluated, since prolonged daily ingestion of large quantities of these compounds as dietary supplements is known to occur.

In the fall of 1990, LSRO initiated the study by first searching the extant scientific literature for reports that related to the safety of amino acids. During February 1991, LSRO sponsored an open meeting where interested parties could present information and views related to this issue (U.S.

Food and Drug Administration, 1990). Eight individuals made oral presentations, and 30 individuals or organizations later submitted written materials for consideration by LSRO. Following these activities, an ad hoc expert panel consisting of nine scientists was assembled.

The panel met on four occasions during the subsequent year to advise LSRO on the adequacy of the available materials and to prepare a final report. In addition to assessing safety on the basis of information in the present literature, the report also contained suggested guidelines for future safety evaluations.

This report was made available in the summer of 1992 (Anderson and Raiten, 1992).

The use of amino acids as dietary supplements created a serious dilemma in the evaluation of safety, since these substances are used primarily by consumers for presumed pharmacological purposes or for the enhancement of physiological function rather than for any nutritional purposes.

There was no evidence available in the literature indicating that a normal, healthy individual would benefit nutritionally in any way from supplementation of the diet with a single amino acid.

Even in those individuals with a less than ideal diet, the practice of supplementing the diet with single amino acids was considered potentially dangerous. Additionally, the literature was replete with studies demonstrating “antinutritional” effects (i.e.

, depressed growth and other adverse effects) associated with the intake of imbalanced amino acid diets (Benevenga and Steele, 1984).

Products in the marketplace that were surveyed were characterized by a wide diversity of label information and generally failed to provide the required information regarding chemical composition, isomeric identification, purity, shelf-life and contraindications to use.

For instance, although some labels of products containing L-phenylalanine warned patients with phenylketonuria, others failed to do so.

The potential for adverse effects associated with the ingestion of this amino acid in patients with this inherited metabolic abnormality are well documented (Lenke and Levy, 1980; Matalon et al., 1991).

Although manufacturers carefully avoid legal drug claim language on labels and advertising, many product labels and advertisments clearly suggested that such products provided pharmacological rather than nutritional benefit. No reliable information was available to accurately assess the patterns of consumption of these supplements in the U.S. population.

The expert panel was aware of the use of D-amino acids as dietary supplements and concluded that such a practice was clearly inappropriate because these enantiomerically related amino acids have generally been shown to provide no nutritional support for humans and, in many cases, are potent toxicants (Friedman, 1991).

Concern was also expressed regarding the interaction between amino acids used as dietary supplements and over-the-counter and prescription drugs, as this constitutes an area not adequately investigated to date.

There are numerous examples in the literature detailing observed or potential interactions between these amino acids and monoamine oxidase inhibitors, many antidepressants, sympathomimetic amines, and opioids (Glassman and Platman, 1969; Hull and Maher, 1990).

As part of the scope of work associated with the FASEB/LSRO investigation, some estimate of the safe upper level of intake for each individual amino acid was requested.

The expert panel was unable to identify a safe upper level for any of the amino acids considered, beyond that normally found in typical proteins.

Additionally, the only safe form of amino acid ingestion was considered to be via protein in the diet.

As a result of the paucity of available information bearing upon the safety of amino acids used as dietary supplements, the ad hoc expert panel concluded that a systematic approach to safety testing was needed. The proposed testing should involve studies in both animals and humans and should employ a two-tiered approach.

In the first tier, studies with animals should investigate the effects of acute and chronic ingestion of amino acids.

Such studies would include the determination of weight changes, food intake, neurological and behavioral changes, liver function, routine blood chemistry and hematological parameters, hormonal changes, and pharmacokinetic profiles following oral administration of the amino acid with and without food in both sexes.

Multiple observation points would be used throughout the studies, and various doses would be employed. The expert panel suggested doses of 3, 10, 30, and 100 times the nutritional requirements for indispensable amino acids and 3, 10, 30 and 100 times the levels permitted for protein fortification for the dispensible amino acids (21 CFR 172.320).

Teratologic and developmental effects would also be ascertained simultaneously during this preliminary testing phase. On the basis of the findings of those studies and the existing literature, specialized studies would then be performed during the second tier. The second-tier studies would include functional assessment and gross pathological examinations.

Following studies in animals, acute and chronic testing in humans would be required to satisfy additional safety concerns.

Growth, neurological and behavioral function, hematological parameters, pharmacokinetic profiles, and hormonal changes would be monitored following exposure to various doses of the selected amino acids.

Although initial studies should be carried out in normal healthy adult volunteers, additional studies should use selected groups of individuals who might be expected to use the particular amino acid, e.g., athletes and bodybuilders. Since certain subsets of the population, e.g.

, infants, children, adolescents, pregnant and lactating women, and elderly individuals, might be expected to be at greater risk of adverse effects from ingestion of particular amino acids, they should be excluded from such studies. Additionally, persons with specific diseases or conditions, e.g.

, diabetes mellitus, endocrine disorders, hepatic disease, or other conditions, should similarly be excluded from this phase of investigation. Special precautions would be required to address safety concerns in these subgroups, and studies in these subgroups should be performed only after a reasonable degree of safety has been established.

The FASEB/LSRO report on the safety of amino acids as dietary supplements concluded the following:

  • There is no nutritional rationale to the use of amino acids as dietary supplements, and such a practice can be dangerous.
  • Supplemental amino acids are used for pharmacological rather than nutritional purposes.
  • Currently available labeling fails to supply the required information on a routine basis.
  • The extant scientific literature fails to support a safe upper limit for supplementation with any amino acid beyond that found in protein.
  • There are several subsets of the population that are ly to be more sensitive to the adverse effects of amino acid supplementation.
  • Systematic testing in animals and humans is required before the safety of supplemental amino acids can be adequately assessed.

It is therefore recommended by this author that any approach to the fortification of military rations with supplemental amino acids beyond those levels found in protein should be considered a pharmacological intervention and not merely a nutritional manipulation, and thus should be initiated with appropriate caution to safeguard the welfare of those who consume military rations.


Timothy J.Maher, Professor and Chairman, Department of Pharmacology, Massachusetts College of Pharmacology, 179 Longwood Avenue, Boston, MA 02115



Phenylalanine: Potential Benefits + Foods & Side Effects

Phenylketonuria (PKU) is a rare but potentially serious inherited disorder.

Our bodies break down the protein in foods, such as meat and fish, into amino acids, which are the “building blocks” of protein.

These amino acids are then used to make our own proteins. Any amino acids that are not needed are broken down further and removed from the body.

People with PKU cannot break down the amino acid phenylalanine, which then builds up in their blood and brain. This can lead to brain damage.

At around 5 days old, babies are offered newborn blood spot screening to test for PKU and many other conditions. This involves pricking your baby's heel to collect drops of blood to test.

If PKU is confirmed, treatment will be given straight away to reduce the risk of serious complications. Treatment includes a special diet and regular blood tests.

With early diagnosis and the correct treatment, most children with PKU are able to live healthy lives.

About 1 in 10,000 babies born in the UK has PKU.

PKU does not usually cause any symptoms if treatment is started early.

Without treatment, PKU can damage the brain and nervous system, which can lead to learning disabilities.

Other symptoms of untreated PKU include:

  • behavioural difficulties such as frequent temper tantrums and episodes of self-harm
  • fairer skin, hair and eyes than siblings who do not have the condition (phenylalanine is involved in the body's production of melanin, the pigment responsible for skin and hair colour)
  • eczema 
  • repeatably being sick
  • jerking movements in arms and legs
  • tremors 
  • epilepsy
  • musty smell to the breath, skin and urine

The main treatment for PKU is a low-protein diet that completely avoids high-protein foods (such as meat, eggs and dairy products) and controls the intake of many other foods, such as potatoes and cereals.

In addition, people with PKU must take an amino acid supplement to ensure they're getting all the nutrients required for normal growth and good health.

There are also several low-protein versions of common foods (such as flour, rice and pasta) specifically designed for people with PKU and related conditions to incorporate into their diets. Many of these are available on prescription.

If a high phenylalanine level is confirmed, a baby will immediately be started on a low-protein diet and amino acid supplements.

Phenylalanine levels are regularly monitored by collecting blood from a finger prick on to a special card and sending it to a laboratory.

A dietitian will create a detailed dietary plan for your child that can be revised as your child grows and their needs change.

As long as a person with PKU sticks to a low-protein diet throughout childhood, and their phenylalanine levels stay within certain limits, they'll remain well and their natural intelligence will be unaffected.


People with PKU must also avoid food products that contain aspartame, as it's converted into phenylalanine in the body.

Aspartame is a sweetener found in:

  • sugar substitutes such as the artificial sweeteners often used in tea and coffee
  • diet versions of fizzy drinks
  • chewing gum
  • squash and cordial
  • some alcopops

All food products that contain aspartame or a related product should be clearly labelled.

There are also medicines that contain aspartame, such as some children's cold and flu remedies.

It's a legal requirement for any medicine that contains aspartame to state it on the patient information leaflet that comes with the medicine.

Regular blood tests

A child with phenylketonuria will need regular blood tests to measure levels of phenylalanine in their blood and assess how well they're responding to treatment.

Only a drop of blood is needed, and it can be collected at home and sent to the hospital by post.

You may be able to have training so you can do your child's blood tests, or be able to test yourself if you have PKU. This will make testing more convenient.

It's recommended that children who are:

  • 6 months of age or younger should have their blood tested once a week
  • between 6 months and 4 years of age should have their blood tested once every 2 weeks
  • over 4 years of age should have their blood tested once a month

Someone with PKU will usually need to have regular blood tests throughout their life.

The genetic cause (mutation) responsible for PKU is passed on by the parents, who are usually carriers and do not have any symptoms of the condition themselves.

The way this mutation is passed on is known as autosomal recessive inheritance. This means a baby needs to receive 2 copies of the mutated gene to develop the condition – 1 from their mother and 1 from their father.

If the baby only receives 1 affected gene, they'll just be a carrier of PKU.

If you're a carrier of the altered gene and you have a baby with a partner who's also a carrier, your baby has:

  • a 1 in 4 chance of inheriting the condition
  • a 1 in 2 chance of being a carrier of PKU
  • a 1 in 4 chance of receiving a pair of normal genes

Many adults with PKU find they function best while on a low-protein diet. The current advice is for people with PKU to remain on a low-protein diet for life.

Un in young children, there is not yet any evidence that high phenylalanine levels cause any permanent brain damage in adults with PKU.

Some adults with PKU may have higher phenylalanine levels because they find it difficult to follow the low-protein diet or have returned to a normal diet.

As a result, they may find they do not function as well. For example, they may lose concentration or have a slower reaction time.

These adverse effects can usually be reversed by going back on to a strict diet to bring the phenylalanine levels down again.

Anyone who returned to a normal diet should still be supported by their clinicians and have a regular follow-up to monitor their condition for any complications that might arise.

For women with PKU, it's essential that they return to a strict diet if they're considering becoming pregnant, as high phenylalanine levels can harm an unborn child.

Women with PKU must take particular care during pregnancy, as high levels of phenylalanine can damage their unborn baby.

Provided that phenylalanine levels are strictly controlled during pregnancy, problems can be avoided and there's no reason why a woman with PKU should not be able to have a normal, healthy baby.

It's recommended that all women with PKU plan their pregnancies carefully. You should aim to follow a strict low-protein diet and monitor your blood twice a week before becoming pregnant.

It's best to try to conceive once phenylalanine levels are within the target range for pregnancy.

During pregnancy, you'll be asked to provide blood samples 3 times a week and will be in frequent contact with a dietitian.

As soon as your baby is born, phenylalanine control can be relaxed and there's no reason why you cannot breastfeed your baby.

Contact your PKU doctor and dietitian as soon as possible if you become pregnant when your phenylalanine levels are not adequately controlled.

If your phenylalanine levels can be brought under control within the first few weeks of your pregnancy, the risk of damage to your baby should be small. But your pregnancy will need to be monitored very carefully.

Information about you

If you or your child has PKU, your clinical team will pass on information about you to the National Congenital Anomaly and Rare Diseases Registration Service (NCARDRS).

This helps scientists look for better ways to prevent and treat this condition. You can opt the register at any time.

Find out more about the NCARDRS register


Phenylalanine Benefits for Mental Health (Plus, Dosage and More)

Phenylalanine: Potential Benefits + Foods & Side Effects

Have you heard of the amino acid phenylalanine? This crucial compound is absolutely vital for several aspects of health and plays a central role in maintaining normal growth and development.

It’s also important for the synthesis of certain hormones and neurotransmitters that are involved in regulating mood and body weight.

So what is the purpose of phenylalanine? Is phenylalanine the same thing as aspartame, and does phenylalanine increase dopamine?

Keep reading for everything you need to know about this essential amino acid.

What Is Phenylalanine? (Role in Body)

According to Merriam-Webster, the official phenylalanine definition is “an essential amino acid C9H11NO2 that is converted in the normal body to tyrosine.” And much other amino acids L-alanine, arginine and leucine, phenylalanine is considered an important building block that is used to form the proteins that your body needs to function and thrive.

Because it’s considered “essential,” your body is unable to produce it on its own and needs to obtain it from food or supplemental sources instead.

“Phe” is the official phenylalanine abbreviation and, chemically speaking, the phenylalanine structure is aromatic, and it’s considered neutral.

Is phenylalanine polar? Because of its benzyl side chain, the Phe amino acid is considered non-polar and hydrophobic.

This amino acid is used to make many other important compounds, including tyrosine, dopamine, norepinephrine and epinephrine. Emerging research also shows that this key amino acid could play a role in the treatment of several conditions, including depression, Parkinson’s disease and chronic pain.

There are some who may have issues with phenylalanine metabolism, however, and may not be able to process or break it down efficiently. For these individuals, consuming excess amounts can cause serious side effects, ranging from seizures to developmental delays and beyond.

1. Used to Produce Other Compounds

other amino acids, phenylalanine plays a vital role in the production of other key compounds that are important to health. For example, it’s used to produce dopamine, a neurotransmitter that is involved in learning, memory and emotion.

The body also converts phenylalanine to tyrosine, an amino acid that aids in the synthesis of proteins. It’s also involved in the production of norepinephrine and epinephrine, both of which are neurotransmitters released by the body in response to stressful situations.

A deficiency in this important amino acid can cause a long list of symptoms, including confusion, depression, memory loss and low energy levels.

2. May Reduce Symptoms of Depression

One of the top L-phenylalanine benefits is its ability to improve mood and protect against depression. Although more research is needed, some studies have found that it could have powerful mood-boosting properties.

In fact, a study published in the Journal of Neural Transmission found that administering 75–200 milligrams of DL-phenylalanine (DLPA) per day to 20 people improved several symptoms of depression, including overall mood and agitation. Another study found that combining L-phenylalanine with L-deprenyl, a medication used to prevent the breakdown of dopamine, had a beneficial effect on symptoms of depression in 90 percent of outpatient participants.

3. Could Aid in Treatment of Parkinson’s Disease

Parkinson’s disease is a condition that affects the central nervous system, causing symptoms tremors, stiffness and slow movement. According to a study in the International Journal of General Medicine, Parkinson’s disease is also characterized by a depletion of tyrosine, dopamine and norepinephrine, all of which are synthesized from phenylalanine.

Although one study did find that phenylalanine could be therapeutic in the treatment of Parkinson’s disease, additional high-quality human trials should be conducted to determine how it may impact symptoms.

4. Relieves Chronic Pain

Some research has found that phenylalanine could act as a natural pain reliever to help reduce and manage chronic pain. One study even reported that it has been shown to have analgesic properties in both human and animal trials, noting that it may help reduce pain caused by a variety of conditions.

Another animal study showed that injecting horses with a combination of amino acids, including D-phenylalanine and D-leucine, helped reduce chronic pain by preserving the activity of specific endorphins in the brain.

5. May Promote Weight Loss

Does L-phenylalanine help with weight loss? While more studies on the link between L-phenylalanine and weight loss are definitely needed, some emerging evidence shows that phenylalanine could have a big impact when it comes to your waistline.

A study conducted by the Department of Gastroenterology at St.

Bartholomew’s Hospital in London actually found that administering L-phenylalanine to 10 participants before meals reduced food intake and increased levels of cholecystokinin (CCK), a hormone that stimulates digestion and helps keep appetite under control.

Another in vitro study in the American Journal of Physiology had similar findings, noting that phenylalanine was able to increase secretion of CCK, which could potentially aid in weight loss.

Risks and Side Effects

Is phenylalanine bad for your health? For most people, it’s safe and associated with very few adverse side effects.

Although it’s found naturally in many foods, it’s also sometimes added to products as well. other amino acids, phenylalanine is generally recognized as safe by the Food and Drug Administration when used as a food additive.

In supplement form, it has been shown to be well-tolerated in doses up to 45 milligrams per pound of body weight. Some of the most common side effects associated with high doses include nausea, heartburn, fatigue, headaches, constipation and anxiety.

Phenylalanine supplements are not recommended for women who are pregnant or breastfeeding, as research is limited on the safety for these specific populations. Those with schizophrenia should also avoid taking phenylalanine as it may cause tardive dyskinesia, a disorder characterized by involuntary and repetitive movements.

Furthermore, those with phenylketonuria (PKU) need to be mindful of phenylalanine intake. PKU is a birth defect and form of phenylalanine hydroxylase deficiency that impairs the body’s ability to process phenylalanine efficiently, resulting in a build-up in the blood.

Why is phenylalanine build-up bad, and what happens when phenylalanine accumulates in the body? Left untreated, PKU can cause growth failure, seizures, developmental delays and mental disability.

Phenylketonurics are generally advised to follow a low-protein, low-phenylalanine diet, which helps limit their intake of foods with phenylalanine to prevent side effects.

Is phenylalanine bad for diabetics? And is this amino acid safe and effective for the general population?

For most adults, there are very few phenylalanine dangers or side effects to consider. In fact, this amino acid is an important part of the diet and essential for the production of several hormones and neurotransmitters.

However, it is important to get your this amino acid from natural sources rather than artificial sweeteners aspartame.

What are the negative effects of aspartame? There’s a lot of controversy about potential aspartame dangers, with research suggesting that non-nutritive sweeteners may impact cancer growth and gut health.

Other possible aspartame effects include alterations in brain function and metabolic health.

Those with PKU also need to be mindful of their intake. This disorder impairs the body’s ability to process phenylalanine efficiently, which can cause excess levels to build up in the blood.

Potential phenylalanine effects for those with PKU may include mental disabilities, developmental delays and seizures.

Taking phenylalanine or dopamine supplements is not recommended for those taking other psychiatric medications or women who are pregnant or breastfeeding. It’s also not recommended for those taking Baclofen, as it may decrease its absorption.

As an antispasmodic medication, Baclofen uses include treating muscle spasms, stiffness and pain.

Foods and Supplements

Phenylalanine is found naturally in a wide array of food sources, including both plant-based and animal-based protein sources. Meat, fish and poultry are a few of the most common foods high in phenylalanine, along with eggs, nuts, seeds and soy products.

Rather than focusing on filling your plate with phenylalanine foods, however, it’s best to simply focus on incorporating a variety of nutrient-dense protein foods into your diet.

As a food additive, you can also find phenylalanine in gum, soda and other diet products. This is because phenylalanine is found in aspartame, which is often used as a calorie-free sugar substitute in many low-calorie products.

What is aspartame? Is aspartame bad for you?

Aspartame is an artificial sweetener made up of aspartic acid and phenylalanine. Although it has been approved for use by the FDA, serious questions have been raised regarding its safety recently.

In particular, aspartame and other artificial sweeteners have been studied for their potential effects on metabolic health and the gut microbiome, as well as their role in other issues cancer and mental disorders. Fortunately, it’s easy to find gum without aspartame, and there are plenty of other natural sugar substitutes you can enjoy instead as part of a healthy diet.

Phenylalanine supplements are also available for those looking for methods for how to increase dopamine with supplements. These supplements are usually found in powder or capsule form and have several potential uses, but are primarily used to boost mood and mental clarity.

How to Use It (and Proper Dosage)

Ideally, you should be able to meet the majority of your amino acid needs through food sources alone. If you do opt to take a phenylalanine supplement, be sure to use only as directed and consult with your doctor if you’re taking other medications or have any underlying health conditions.

These supplements are not recommended for those using antidepressants or other psychiatric medications, as they may cause adverse side effects or interactions.

It’s best to take supplements on an empty stomach, about an hour or so before eating to maximize absorption. Most supplement manufacturers advise taking around 1,000–1,500 milligrams daily,  which is typically divided into three or four smaller doses.


Looking for an easy way to get your fix of natural dopamine by upping your intake of phenylalanine? Try incorporating a few of these high-protein, dopamine foods into your daily diet:

Final Thoughts

  • The phenylalanine amino acid is an essential amino acid that is important for growth and development as well as the production of several neurotransmitters and hormones.
  • Some studies suggest this amino acid could promote weight loss, reduce chronic pain, decrease symptoms of Parkinson’s disease and protect against depression.
  • In addition to being found in protein foods, it’s also a component of aspartame. For this reason, you can find it in soda, chewing gum and many diet products.
  • However, because of the potential aspartame dangers, it’s best to meet your needs primarily through whole food sources instead.
  • This amino acid is found naturally in many food sources and can be safely consumed by most people without any adverse effects. However, those with PKU need to limit their intake and follow a special low-protein diet to keep blood levels normal.