|Also Known As:
|| D-phenylalanine, L-Phenylalanine,
Phenylalanine is an essential amino acid, which means that it is essential to
human health but cannot be manufactured by the body. For this reason,
phenylalanine must be obtained from food. Amino acids are the building blocks of
protein. It is available in three chemical forms: L-phenylalanine, the natural
form of phenylalanine found in proteins throughout the body; (2)
D-phenylalanine, a mirror image of L-phenylalanine that is synthesized in a
laboratory; and (3) DL-phenylalanine, a combination of the previous two
The body converts phenylalanine into tyrosine, another amino acid essential
for making proteins, certain brain chemicals, and thyroid hormones. Symptoms of
phenylalanine deficiency include confusion, lack of energy, decreased alertness,
decreased memory, and diminished appetite.
On the other hand, a rare metabolic disorder called phenylketonuria (PKU)
occurs in people who are missing an enzyme that is needed to properly metabolize
phenylalanine. Symptoms of PKU, which tend to appear between three and six
months of age, include eczema, developmental delay, an abnormally small head,
and hyperactivity. If it is not treated before three weeks of age, PKU can cause
severe, irreversible mental retardation. In the United States, newborns are
tested for PKU during the first 48 to 72 hours of life.
People with PKU must eat a phenylalanine-restricted, tyrosine-supplemented
diet to have optimum brain development and growth. Rarely, over-restriction of
phenylalanine in the diet can lead to deficiency of this amino acid, with the
same symptoms described above.
Although results of studies have not been
entirely consistent, preliminary evidence suggests that D-phenylalanine may help
reduce chronic pain associated with certain health conditions by stimulating
nerve pathways in the brain that control pain. Some scientists, for example,
report that they have observed enhanced pain relief when D-phenylalanine is used
together with prescription pain-killers. Other studies have found
D-phenylalanine to be no more effective than placebo in reducing pain. Further
research is needed to determine the safety and effectiveness of this amino acid
One animal study suggests that
D-phenylalanine may improve rigidity, walking disabilities, speech difficulties,
and depression associated with Parkinson's disease. It is not clear whether
these results translate into a possible treatment for people with this disease,
however. Further studies in people are necessary before supplementation with
this amino acid can be recommended for individuals with Parkinson's disease.
Evidence suggests that combining L-phenylalanine
(oral and topical) with UVA radiation for people with vitiligo (a condition
characterized by irregular depigmentation or white patches of skin) may lead to
some darkening or repigmentation of the whitened areas, particularly on the
face. Although preliminary information suggests that it is safe when used under
appropriate medical guidance and supervision, more research is needed to assess
potential side effects of this treatment approach.
Although far from proven, there is at least
theoretic benefit in using phenylalanine as part of a comprehensive therapy for
depression. In support of this theory, some individuals have reported
improvement in mood when taking phenylalanine. This is thought to be due to
enhanced production of brain chemicals such as dopamine and norepinephrine. More
research is needed.
L-phenylalanine is found in most foods that contain protein such as beef,
poultry, pork, fish, milk, yogurt, eggs, cheese, soy products (including soy
protein isolate, soybean flour, and tofu), and certain nuts and seeds. The
artificial sweetener aspartame is also high in phenylalanine.
D-phenylalanine is synthesized in the laboratory is not found in food.
- DL-phenylalanine (50/50 blend of D-phenylalanine and L-phenylalanine)
Phenylalanine can be taken as a capsule, powder, or tablet or used as a
|How to Take It|
Recommended dosages of phenylalanine vary depending on the health condition
being treated. Supplements are recommended 15 to 30 minutes before meals.
According to the National Research Council, the daily recommended dietary
allowances (RDAs) for phenylalanine are as follows:
- Birth to 4 months: 125 mg per kilogram of body weight per day
- Children 5 months to 2 years: 69 mg per kilogram of body weight per
- Children 3 to 12 years: 22 mg per kilogram of body weight per day
The combination of oral and topical phenylalanine (together with ultraviolet
light) have been used to treat children with vitiligo. The dose and appropriate
length of time to continue the therapy would be determined by your physician.
- Teenagers and adults: 14 mg per kilogram of body weight per day
Some experts suggest that adults may need as much as 39 mg per kilogram of
body weight per day for general health and doses as high as 50 to 100 mg per
kilogram have been used in studies of those with vitiligo. The most common
amounts used range from 750 to 3,000 mg per day for adults.
Because of the potential for side effects and interactions with medications,
dietary supplements should be taken only under the supervision of a
knowledgeable healthcare provider.
People with PKU and women who are lactating or are pregnant should not take
Little is known about the use of aspartame during pregnancy. Talk with your
health care provider about using this artificial sweetener.
DL-phenylalanine may cause symptoms of anxiety, jitteriness, and
hyperactivity in children. Children with ADHD may need to avoid foods containing
aspartame, which is made from phenylalanine.
Doses in excess of 5,000 mg a day may be toxic and can cause nerve damage.
High quantities of DL-phenylalanine may cause mild side effects such as nausea,
heartburn, and headaches.
If you are currently being treated with any of the following medications, you
should not use phenylalanine without first talking to your healthcare
Antidepressant Medications, Monoamine Oxidase Inhibitors
Phenylalanine may cause a severe increase in blood pressure
in people taking MAOIs (such as phenelzine, tranylcypromine, pargyline, and
selegiline). This severe increase in blood pressure (also called
"hypertensive crisis") can lead to a heart attack or stroke. For this reason,
individuals taking MAOIs should avoid foods and supplements containing
The absorption of baclofen, a medication used to
relieve muscle spasms, may be reduced by phenylalanine. Therefore, it is best to
avoid taking this medication with a meal, especially one that is high in protein
content, or with phenylalanine supplements.
A few case reports suggest that phenylalanine may
reduce the effectiveness of levodopa, a medication used to treat Parkinson's
disease. Some researchers speculate that phenylalanine may interfere with the
absorption of this medication. Therefore, phenylalanine should not be taken at
the same time as levodopa.
Antoniou C, Katsambas A. Guidelines for the treatment of vitiligo.
Bugard P, Bremer HJ, Buhrdel P, et al. Rationale for the German
recommendations for phenylalanine level control in phenylketonuria 1997. Eur
J Pediatr. 1999;158:46-54.
Burkhart CG, Burkhart CN. Phenylalanine with UVA for the treatment of
vitiligo needs more testing for possible side effects. J Am Acad
Dermatol. 1999;40(6 Pt 1):1015.
Camacho F, Mazuecos J. Treatment of vitiligo with oral and topical
phenylalanine: 6 years of experience. Arch Dermatol. 1999;135(2):216-217.
Cejudo-Ferragud E, Nacher A, Polache A, Ceros-Fortea T, Merino M, Casabo VG.
Evidence of competitive inhibition for the intestinal absorption of baclofen by
phenylalanine. Int J Pharmaceutics. 1996;132:63-69.
Cormane RH, Siddiqui AH, Westerhof W, Schutgens RB. Phenylalanine and UVA
light for the treatment of vitiligo. Arch Dermatol Res.
Fugh-Berman A, Cott JM. Dietary supplements and natural products as
psychotherapeutic agents. Psychomatic Med. 1999;61:712-728.
Kovacs SO. Vitiligo. J Am Acad Dermatol. 1998 May;38(5 Pt
Meyers S. Use of neurotransmitter precursors for treatment of depression.
Alt Med Rev. 2000;5(1):64-71.
Pietz J. Neurological aspects of adult phenylketonuria. Curr Opin
Pietz J, Dunckelmann R, Rupp A, et al. Neurological outcome in adult patients
with early-treated phenylketonuria. Eur J Pediatr.
Rezvani I. Defects in metabolism of amino acids; Phenylalanine. In: Behrman
RE, Kliefman RM, and Jenson HB, eds. Nelson Textbook of Pediatrics. 16th
ed. Philadelphia, PA: W.B. Saunders Company; 2000: 344-346.
Russell AL, McCarty MF. DL-phenylalanine markedly potentiates opiate
analgesia - an example of nutrient pharmaceutical
up-regulation of the endogenous analgesia system. Med Hypotheses.
Sabelli HC, Fawcett J, Gusovsky F, et al. Clinical studies on the
phenylethylamine hypothesis of affective disorder: urine and blood phenylacetic
acid and phenylalanine dietary supplements. J Clin Psychiatry.
Schallreuter KU, Zschiesche M, Moore J, et al. In vivo evidence for
compromised phenylalalanine metabolism in vitiligo. Biochem Biophys Res
Schulpis CH, Antoniou C, Michas T, Strarigos J. Phenylalanine plus
ultraviolet light: preliminary report of a promising treatment for childhood
vitiligo. Pediat Dermatol. 1989;6(4):332-335.
Shils ME, Olson JA, Shike M, Ross AC. Modern Nutrition in Health and
Disease. 9th ed. Baltimore, Md: Williams & Wilkins; 1999(41):1010.
Siddiqui AH, Stolk LM, Bhaggoe R, et al. L-phenylalanine and UVA irradiation
in the treatment of vitiligo. Dermatology. 1994;188(3):215-218.
Start K. Treating phenylketonuria by a phenylalanine-free diet. Prof Care
Mother Child. 1998;8:109-110.
Walsh NE, Ramamurthy S, Schoenfeld L, Hoffman J. Analgesic effectiveness of
D-phenylalanine in chronic pain patients. Arch Phys Med Rehabil.
Werbach MR. Nutritional Influences on Illness. 2nd ed. Tarzana, Calif:
Third Line Press; 1993:159-160, 384, 434,
494-495, 506, 580, 613-614,
Woodward WR, Olanow CW, Beckner RM, et al. The effect of L-dopa infusions
with and without phenylalanine challenges in parkinsonian patients: Plasma and
ventricular CSF L-dopa levels and clinical responses. Neurol.
|Review Date: April 2002|
|Reviewed By: Participants in the review process include: Jacqueline A. Hart, MD,
Department of Internal Medicine, Newton-Wellesley Hospital, Harvard University
and Senior Medical Editor Integrative Medicine, Boston, MA; Gary Kracoff, RPh
(Pediatric Dosing section February 2001), Johnson Drugs, Natick, Ma; Steven
Ottariono, RPh (Pediatric Dosing section February 2001), Veteran's
Administrative Hospital, Londonderry, NH; Margie Ullmann-Weil, MS, RD,
specializing in combination of complementary and traditional nutritional
therapy, Boston, MA. All interaction sections have also been reviewed by a team
of experts including Joseph Lamb, MD (July 2000), The Integrative Medicine
Works, Alexandria, VA;Enrico Liva, ND, RPh (August 2000), Vital Nutrients,
Middletown, CT; Brian T Sanderoff, PD, BS in Pharmacy (March 2000), Clinical
Assistant Professor, University of Maryland School of Pharmacy; President, Your
Prescription for Health, Owings Mills, MD; Ira Zunin, MD, MPH, MBA (July 2000),
President and Chairman, Hawaii State Consortium for Integrative Medicine,
Copyright © 2004 A.D.A.M., Inc
The publisher does not accept any responsibility for the accuracy of
the information or the consequences arising from the application, use, or misuse
of any of the information contained herein, including any injury and/or damage
to any person or property as a matter of product liability, negligence, or
otherwise. No warranty, expressed or implied, is made in regard to the contents
of this material. No claims or endorsements are made for any drugs or compounds
currently marketed or in investigative use. This material is not intended as a
guide to self-medication. The reader is advised to discuss the information
provided here with a doctor, pharmacist, nurse, or other authorized healthcare
practitioner and to check product information (including package inserts)
regarding dosage, precautions, warnings, interactions, and contraindications
before administering any drug, herb, or supplement discussed