Phenylalanine is an essential amino acid (a building block for proteins in the body), meaning the body needs it for health but cannot make it. You have to get it from food. Phenylalanine is found in 3 forms: L-phenylalanine, the natural form found in proteins; D-phenylalanine (a mirror image of L-phenylalanine that is made in a laboratory), and DL-phenylalanine, a combination of the 2 forms.
The body changes phenylalanine into tyrosine, another amino acid that's needed to make proteins, brain chemicals, including L-dopa, epinephrine, and norepinephrine, and thyroid hormones. Because norepinephrine affects mood, different forms of phenylalanine have been proposed to treat depression. Symptoms of phenylalanine deficiency include confusion, lack of energy, depression, decreased alertness, memory problems, and lack of appetite.
On the other hand, a rare metabolic disorder called phenylketonuria (PKU) occurs in people who are missing an enzyme that the body needs to use phenylalanine. That causes high levels of phenylalanine to build up. If it is not treated before 3 weeks of age, PKU can cause severe, irreversible intellectual disability. In the United States, newborns are tested for PKU during the first 48 - 72 hours of life.
People with PKU must eat a diet that avoids phenylalanine and take tyrosine supplements to have optimum brain development and growth.
D-phenylalanine (but not L-phenylalanine) has been proposed to treat chronic pain, but so far the studies have not shown good evidence that it works. Two studies that appeared to show positive results had flaws that made the findings unreliable. Other clinical studies have found D-phenylalanine to be no more effective than placebo in reducing pain. No randomized controlled trials have been done in the past 20 years to study any possible benefit of taking D-phenylalanine for chronic pain, so more research is needed to determine its safety and effectiveness.
One animal study suggests that D-phenylalanine may improve rigidity, walking disabilities, speech difficulties, and depression associated with Parkinson's disease. However, there is no evidence yet whether it would have the same effect in humans. More research is needed.
Some preliminary studies have found that L-phenylalanine (oral and topical) strengthens the effect of UVA radiation for people with vitiligo. Vitiligo is a condition where irregular depigmentation (loss of color) causes white patches of skin. L-phenylalanine may lead to some darkening or repigmentation of the white patches, particularly on the face. However, more research is needed to see whether L-phenylalanine is truly effective.
Some clinical studies suggest that phenylalanine may be helpful as part of a comprehensive therapy for depression. However, most of the studies were done in the 1970s and 1980s and were not rigorously tested. People have reported that their mood improved when they took phenylalanine. Researchers think this is because phenylalanine increases production of brain chemicals, such as dopamine and norepinephrine. More research is needed to tell whether phenylalanine has any real effect on depression.
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 made in the laboratory but 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. It can also be used as a topical cream.
How to Take It
Recommended dosages of phenylalanine vary depending on the health condition being treated. Speak to your doctor about what dose is right for you.
Because of the potential for side effects and interactions with medications, you should only take dietary supplements under the supervision of a knowledgeable health care provider.
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. People with PKU should not use aspartame. If you are pregnant, ask your doctor about using this artificial sweetener.
DL-phenylalanine should not be used in people taking antipsychotic drugs, as it may cause or make worse symptoms of tardive dyskinesia (TD). TDs are involuntary movements of the tongue, lips, face, trunk, and limbs that can occur in people taking antipsychotic drugs long term.
DL-phenylalanine may cause symptoms of anxiety, jitteriness, and hyperactivity in children.
Doses higher than 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 health care provider.
Monoamine Oxidase Inhibitors -- Monoamine oxidase inhibitors (MAOIs) are an older class of antidepressants drugs that are rarely used now. They include phenelzine (Nardil), isocarboxazid (Marplan), and tranylcypromine sulfate (Parnate). Taking phenylalanine while taking MAOIs may cause a severe increase in blood pressure (hypertensive crisis). This severe increase in blood pressure can lead to a heart attack or stroke. People taking MAOIs should avoid foods and supplements containing phenylalanine.
Baclofen -- Phenylalanine may reduce absorption of baclofen (Lioresal), a medication used to relieve muscle spasms. Avoid taking Baclofen with a meal, especially one that is high in protein, or with phenylalanine supplements.
Levodopa -- A few case reports suggest that phenylalanine may reduce the effectiveness of levodopa (Sinemet), a medication used to treat Parkinson's disease. Some researchers think phenylalanine may interfere with the absorption of levodopa.
Selegiline -- L-phenylalanine and the selective MAO inhibitor selegiline (Eldepryl, Deprenyl) may strengthen the antidepressant effects of phenylalanine. They should not be taken together.
Antipsychotic or neuroleptic drugs -- L-phenylalanine may worsen tardive dyskinesia, a side effect of these neuroleptic drugs. These drugs include phenytoin (Dilantin), valproic acid (Depakene, Depakote), and carbamazepine (Tegretol), among others.
Camacho F, Mazuecos J. Oral and topical L-phenylalanine, clobetasol propionate, and UVA/sunlight--a new study for the treatment of vitiligo. J Drugs Dermatol. 2002;1(2):127-31.
Dietary Guidelines for Americans 2005. Rockville, MD : US Dept of Health and Human Services and US Dept of Agriculture; 2005.
Dillon EL, Sheffield-Moore M, Paddon-Jones D, Gilkison C, et al. Amino acid supplementation increases lean body mass, basal muscle protein synthesis, and insulin-like growth factor-I expression in older women. J Clin Endocrinol Metab. 2009 May;94(5):1630-7. Epub ahead of print.
Kliegman R. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, PA: Saunders, An Imprint of Elsevier; 2007.
Lotti T, Buggiani G, Troiano M, Assad GB, Delescluse J, De Giorgi V, Hercogova J. Targeted and combination treatments for vitiligo. Comparative evaluation of different current modalities in 458 subjects. Dermatol Ther. 2008 Jul;21 Suppl 1:S20-6.
MacLeod EL, Gleason ST, van Calcar SC, Ney DM. Reassessment of phenylalanine tolerance in adults with phenylketonuria is needed as body mass changes. Mol Genet Metab. 2009; 98(4):331-7.
Poewe W. Treatments for Parkinson disease--past achievements and current clinical needs. Neurology. 2009 Feb 17;72(7 Suppl):S65-73.
Reuss S, Weiss C, Bayerl C. Phenylalanine and UVA for Vitiligo patients: probability of an effective treatment. Med Hypotheses. 2006;67(1):199-200.
Russell AL, McCarty MF. DL-phenylalanine markedly potentiates opiate analgesia - an example of nutrient/pharmaceutical up-regulation of the endogenous analgesia system. Med Hypotheses. 2000;55(4):283-8.
Szczurko O, Boon HS. A systematic review of natural health product treatment for vitiligo. BMC Dermatol. 2008 May 22;8:2. Review.
Steven D. Ehrlich, NMD, Solutions Acupuncture, a private practice specializing in complementary and alternative medicine, Phoenix, AZ. Review provided by VeriMed Healthcare Network.
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