Health Guide


What is it?

Phenylalanine is a dietary supplement used to treat depression, chronic pain, Parkinson's disease, and vitiligo.

Other names for phenylalanine include: L-Phenylalanine and DL-Phenylalanine.

Ask your doctor, nurse, or pharmacist if you need more information about this medicine or if any information in this leaflet concerns you.

Before Using:

Tell your doctor if you

  • are taking medicine or are allergic to any medicine (prescription or over-the-counter (OTC) or dietary supplement)
  • are pregnant or plan to become pregnant while using this medicine
  • are breastfeeding
  • have phenylketonuria (PKU)
  • have any other health problems, such as high blood pressure, heart or blood vessel disease, liver or kidney disease, skin cancer, or tyrosinnemia
  • have had radiotherapy


Talk with your caregiver about how much phenylalanine you should take. The amount depends on the strength of the medicine and the reason you are taking phenylalanine. If you are using this medicine without instructions from your caregiver, follow the directions on the medicine bottle. Do not take more medicine or take it more often than the directions tell you to.

To store this medicine:

Keep all medicine locked up and away from children. Store medicine away from heat and direct light. Do not store your medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down and not work the way it should work. Throw away medicine that is out of date or that you do not need. Never share your medicine with others.

Drug and Food Interactions:

Do not take Phenylalanine without talking to your doctor first if you are taking:

  • Levodopa (Dopar(R), Larodopa(R)) (8-11)
  • Medicine used for depression or Parkinson's disease (monoamine oxidase inhibitors (MAOIs), examples: isocarboxazid (Marplan(R)), phenelzine (Nardil(R)), selegiline (Eldepryl(R)) (12,19,20)
  • Medicine used for mental health (examples: chlorpromazine (Thorazine(R)), clozapine (Clozaril(R)), haloperidol (Haldol(R)), molindone (Moban(R)), olanzapine (Zyprexa(R)), pimozide (Orap(R)), quetiapine (Seroquel(R)), risperidone (Risperdal(R)), thioridazine (Mellaril(R))) (13)


  • Before taking phenylalanine, tell your doctor if you are pregnant or breastfeeding
  • L-Phenylalanine may cause high blood pressure (14)
  • L-Phenylalanine may increase the risk of stroke (a blood clot in the brain) (14)

Side Effects:

Call your doctor right away if you have any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hand, swelling or tingling in your mouth or throat, chest tightness, trouble breathing, or rash.

Other Side Effects:

You may have the following side effects, but this medicine may also cause other side effects. Tell your doctor if you have side effects that you think are caused by this medicine.

  • Constipation (difficulty having a bowel movement), heartburn, and nausea (upset stomach) (18)
  • Headache and dizziness (15, 16)


1. Kitade T, Odahara Y, Shinohara S et al: Studies on the enhanced effect of acupuncture analgesia and acupuncture anesthesia by D-phenylalanine (first report)--Effect on pain threshold and inhibition by naloxone. Acupunct Electrother 1988; 13(2-3):87-97.

2. Birkmayer W, Riederer P, Linauer W et al: L-deprenyl plus L-phenylalanine in the treatment of depression. J Neural Trans 1984; 59(1):81-87.

3. Heller B, Fischer BE & Martin R: Therapeutic action of D-phenylalanine in Parkinson's disease. Arzneimittelforschung 1976; 26(4):577-579.

4. Siddiqui AH, Stolk LML, Bhaggoe R et al: L-phenylalanine and UVA irradiation in the treatment of vitiligo. Dermatol 1994; 188:215-218.

5. Antoniou C, Schulpis H, Michas T et al: Vitiligo therapy with oral and topical phenylalanine with UVA exposure. Int J Dermatol 1989; 28(8):545-547.

6. Kuiters GRR, Hup JM, Siddiqui AH et al: Oral phenylalanine loading and sunlight as source of UVA irradiation in vitiligo on the Caribbean island of Curacao NA. J Trop Med Hyg 1986; 89(3): 149-155.

7. Cormane RH, Siddiqui AH, Westerhof W et al: Phenylalanine and UVA light for the treatment of vitiligo. Arch Dermatol Res 1985; 277(2):126-130.

8. Eriksson T, Granerus AK, Linde A et al: On-off phenomenon in Parkinson's disease: relationship between dopa and other large neutral amino acids in plasma. Neurology 1988; 38(8):1245-1248.

9. Baruzzi A, Contin M, Riva R et al: Influence of meal ingestion time on pharmacokinetics of orally administered levodopa in parkinsonian patients. Clin Neuropharmacol 1987; 10(6):527-537.

10. Juncos JL, Fabbrini G, Mouradian MM et al: Dietary influences on the antiparkinsonian response to levodopa. Arch Neurol 1987; 44(10):1003-1005.

11. Nutt JG, Woodward WR, Hammerstad JP et al: The on-off phenomenon in Parkinson's disease. Relation to levodopa absorption and transport. N Engl J Med 1984; 310(8):483-488.

12. Silkaitis RP & Mosnaim AD: Pathways linking L-phenylalanine and 2-phenylethylamine with p-tyramine in rabbit brain. Brain Res 1976; 114(1):105-115.

13. Gardos G, Cole JO, Matthews JD et al: The acute effects of a loading dose of phenylalanine in unipolar depressed patients with and without tardive dyskinesia. Neuropsychopharmacology 1992; 6(4):241-247.

14. Zhao G: Inherited metabolic aberration of phenylalanine in the family members of patients with essential hypertension and stroke (Chinese). Chung Hua I Hsueh Tsa Chih 1991; 71(7):28:388-390.

15. 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 Psychiat 1986; 47(2):66-70.

16. Fischer E, Heller B, Nachon M et al: Therapy of depression by phenylalanine. Arzneimittelforschung 1975; 25(1):132.

17. Birkmayer W, Riederer P, Linauer W et al: L-deprenyl plus L-phenylalanine in the treatment of depression. J Neural Transm 1984; 59(1):81-87.

18. Mann J, Peselow ED, Snyderman S et al: D-phenylalanine in endogenous depression. Am J Psychiatry 1980; 137(12):1611-1612.

19. Product Information: Marplan(R), isocarboxazid. Roche Laboratories Inc., Nutley, NJ, 1998.

20. Product Information: Nardil(R), phenelzine. Parke-Davis, Morris Plains, NJ, 1994.

Last Updated: 7/4/2018
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites.

All rights reserved