Written by Slawomir (“Swavak”) Gromadzki, MPH

Phenylalanine is one of essential amino acids (building blocks of proteins), meaning the body needs it from food or in the form of supplements as it cannot make it. Phenylalanine is required for the production of tyrosine (another amino acid) and neurotransmitters such as dopamine, epinephrine and norepinephrine. Since dopamine and norepinephrine positively affect mood, phenylalanine has been proposed to be a beneficial nutritional supplement for those who are depressed.

In addition, our body uses phenylalanine to make also other very important chemicals, including L-dopa and thyroid hormones.

Scientific research suggests Phenylalanine has potential to improve our mood and brain function including concentration, memory, and learning abilities, while enhancing overall alertness.


There are three forms of Phenylalanine:

– L-phenylalanine, the natural form found in proteins.

– D-phenylalanine exactly the same as L-phenylalanine but made in a laboratory. D-phenylalanine has been reported to have more pain-relieving effects than the L- form because it inhibits the enzyme that breaks down opioids.

– DL-phenylalanine, a combination of the 2 forms.


Symptoms of phenylalanine deficiency include:  Lack of energy and fatigue, low mood or depression, memory problems, decreased alertness, etc.



Phenylalanine is the precursor of another amino acid tyrosine which is converted into dopamine. Dopamine has great influence on our mood, motivation, learning abilities and plays very important role in many different processes in the brain such as in pain perception and the reward system of the brain. Without enough dopamine we tend to be impatient and chose lower reward now instead of waiting for higher reward later. Increasing phenylalanine can indirectly raise not only dopamine but also noradrenaline and helps regulate adrenaline levels.

Some people try to take tyrosine supplements to increase dopamine and other neurotransmitters but the problem is that tyrosine does not dissolve well in water and for this reason its direct supplementation is not effective. Therefore, increasing phenylalanine concentrations is regarded as much better alternative to produce more dopamine in the body.


Some studies demonstrated that phenylalanine may be helpful as part of treatment for depression. People have reported that their mood improved as a result of taking phenylalanine supplements. Researchers believe this effects is caused by the fact that phenylalanine increases production of brain chemicals, such as dopamine and norepinephrine.


Some studies appeared to show positive results in the ability of D-phenylalanine to reduce chronic pain.


One animal study suggests that D-phenylalanine may improve movement disabilities, depression and speech difficulties associated with Parkinson’s disease.


Studies suggest that Phenylalanine may help suppress appetite by stimulating the production of hormone, cholecystokinin.


When patients start alcohol-detoxification therapies, the stress associated with the withdrawal process results in lower dopamine levels. Phenylalanine can increase dopamine levels thus helping decrease various psychiatric symptoms.


Preliminary studies suggest L-phenylalanine may lead to some darkening of the white patches on the skin of people suffering from vitiligo.


Low dopamine levels are believed to play a role in ADHD. Therefore, it is suggested that increasing dopamine levels by phenylalanine supplementation should help reduce ADHD symptoms. In a study which involved 13 ADHD patients, those that took DL-phenylalanine supplements showed improvements in symptoms such as anger, restlessness, and focus. Unfortunately, three months after the experiment finished, the beneficial effects of taking this supplement disappeared and increasing the dosage showed no beneficial effect.


Tyrosine may benefit menopausal women by regulating and balancing the neurotransmitters dopamine and norepinephrine in the brain.


L-phenylalanine is found in most foods that contain protein, especially soy products (including soy soybean flour, and tofu), and certain nuts and seeds. Make sure you consume only organic and GMO-free soya products.


Recommended dosages of phenylalanine vary depending on the health condition being treated. Speak to your doctor about what dose is right for you.


People with phenylketonuria (PKU), and women who are breastfeeding or are pregnant, should not take phenylalanine supplements. Aspartame, found in artificial sweeteners such as Nutrasweet, is a source of phenylalanine.

DL-phenylalanine should not be used in people taking antipsychotic drugs.

DL-phenylalanine may cause symptoms of anxiety and hyperactivity in children.

If you are currently being treated with medication you should not use phenylalanine without first talking to your health care provider.


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