Background

• Phenylalanine is commercially available as a dietary supplement in the forms of L-phenylalanine, D-phenylalanine, and DL-phenylalanine. L-phenylalanine is an essential amino acid in humans, and proteins contain only this form. According to experts, L-phenylalanine likely is likely safe when consumed in amounts that typically occur in food. The role of D-phenylalanine in humans is unclear. DL-phenylalanine is a synthetic product made of 50% D-phenylalanine and 50% L-phenylalanine.
• Good scientific evidence (reported primarily in the 1970s and 1980s) supports the use of L-phenylalanine or DL-phenylalanine to treat depression. Good scientific evidence also supports the use of L-phenylalanine, in combination with exposure to ultraviolet A light or sunlight, to treat vitiligo, a skin condition characterized by patchy loss of skin pigments.
• The Cari Loder regime is a treatment for multiple sclerosis (MS) that includes phenylalanine, as well as lofepramine (an antidepressant not available in the United States), and intramuscular injections of vitamin B12. The treatment was developed by Cari Loder, a research scientist and MS patient, and it was described in the popular literature. Subsequent clinical research failed to produce data supporting the use of the regime to treat MS.
• Areas of current research interest regarding phenylalanine include diagnosis, dietetics, nutrition, and physiology.

References

1. Boirie Y, Albright R, Bigelow M, et al. Impairment of phenylalanine conversion to tyrosine in end-stage renal disease causing tyrosine deficiency. Kidney Int 2004;66(2):591-596. View Abstract
2. Camacho F, Mazuecos J. Treatment of vitiligo with oral and topical phenylalanine: 6 years of experience. Arch Dermatol 1999;135(2):216-217. View Abstract
3. 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):127-131. View Abstract
4. Darling PB, Dunn M, Gilani GS, et al. Phenylalanine kinetics differ between formula-fed and human milk-fed preterm infants. J Nutr 2004;134(10):2540-2545. View Abstract
5. Durham WJ, Miller SL, Yeckel CW, et al. Leg glucose and protein metabolism during an acute bout of resistance exercise in humans. J Appl Physiol 2004;97(4):1379-1386. View Abstract
6. Fernstrom JD, Fernstrom MH. Tyrosine, phenylalanine, and catecholamine synthesis and function in the brain. J Nutr 2007;137(6 Suppl 1):1539S-1547S. View Abstract
7. Festi D, Capodicasa S, Sandri L, et al. Measurement of hepatic functional mass by means of 13C-methacetin and 13C-phenylalanine breath tests in chronic liver disease: comparison with Child-Pugh score and serum bile acid levels. World J Gastroenterol 2005;11(1):142-148. View Abstract
8. Koch R, Hanley W, Levy H, et al. The Maternal Phenylketonuria International Study: 1984-2002. Pediatrics 2003;112(6 Pt 2):1523-1529. View Abstract
9. Levy HL, Waisbren SE, Guttler F, et al. Pregnancy experiences in the woman with mild hyperphenylalaninemia. Pediatrics 2003;112(6 Pt 2):1548-1552. View Abstract
10. Moats RA, Moseley KD, Koch R, et al. Brain phenylalanine concentrations in phenylketonuria: research and treatment of adults. Pediatrics 2003;112(6 Pt 2):1575-1579. View Abstract
11. Mosnik DM, Spring B, Rogers K, et al. Tardive dyskinesia exacerbated after ingestion of phenylalanine by schizophrenic patients. Neuropsychopharmacology 1997;16(2):136-146. View Abstract
12. Okano Y, Hase Y, Kawajiri M, et al. In vivo studies of phenylalanine hydroxylase by phenylalanine breath test: diagnosis of tetrahydrobiopterin-responsive phenylalanine hydroxylase deficiency. Pediatr Res 2004;56(5):714-719. View Abstract
13. Thompson P, Balis F, Serabe BM, et al. Pharmacokinetics of phenylacetate administered as a 30-min infusion in children with refractory cancer. Cancer Chemother Pharmacol 2003;52(5):417-423. View Abstract
14. Wade DT, Young CA, Chaudhuri KR, et al. A randomised placebo controlled exploratory study of vitamin B-12, lofepramine, and L-phenylalanine (the "Cari Loder regime") in the treatment of multiple sclerosis. J Neurol Neurosurg Psychiatry 2002;73(3):246-249. View Abstract
15. Widaman KF, Azen C. Relation of prenatal phenylalanine exposure to infant and childhood cognitive outcomes: results from the International Maternal PKU Collaborative Study. Pediatrics 2003;112(6 Pt 2):1537-1543. View Abstract