Herbs & Supplements:
Phenylalanine
Supplement Forms / Alternate Names
•
L-Phenylalanine, D-Phenylalanine, DL-Phenylalanine
Principal Proposed Uses
•
Depression
Other Proposed Uses
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Chronic Pain, Rheumatoid Arthritis, Muscle Pain, Osteoarthritis, Vitiligo, Multiple Sclerosis, Parkinson's Disease, Attention Deficit Disorder
Phenylalanine occurs in two chemical forms: L-phenylalanine, a natural amino acid found in proteins; and its mirror image, D-phenylalanine, a form synthesized in a laboratory. Some research has involved the L-form, others the D-form, and still others a combination of the two known as DL-phenylalanine.
In the body, phenylalanine is converted into another amino acid called tyrosine. Tyrosine in turn is converted into L-dopa, norepinephrine, and epinephrine, three key neurotransmitters (chemicals that transmit signals between nerve cells). Because some antidepressants work by raising levels of norepinephrine, various forms of phenylalanine have been tried as a possible treatment for depression.
D-phenylalanine (but not L-phenylalanine) has been proposed to treat chronic pain. It blocks enkephalinase, an enzyme that may act to increase pain levels in the body. Phenylalanine (various forms) has also been suggested as a treatment for vitiligo, a disease characterized by abnormal white blotches of skin due to loss of pigmentation.
Requirements/Sources
L-phenylalanine is an essential amino acid, meaning that we need it for life and our bodies can't manufacture it from other chemicals. It is found in protein-rich foods such as meat, fish, poultry, eggs, dairy products, and beans. Provided you eat enough protein, you are likely to get enough L-phenylalanine for your nutritional needs. There is no nutritional need for D-phenylalanine.
Therapeutic Dosages
D- or DL-phenylalanine are typically taken at a dose of 100 to 200 mg daily for the treatment of depression.1 For the treatment of chronic pain, usual recommended dosages of D-phenylalanine are as high as 2,500 mg daily.
It is best not to take your phenylalanine supplement at the same time as a high-protein meal, as it may not be absorbed well.
Therapeutic Uses
Preliminary studies suggest that both the D- and DL- forms of phenylalanine may be helpful for depression.2,3
Weak evidence suggests that D-phenylalanine may be useful for chronic pain,4 such as rheumatoid arthritis, muscle pain, and osteoarthritis, but this conclusion has been contested.5,6,7
Preliminary uncontrolled and double-blind studies found that the combination of phenylalanine and ultraviolet radiation might be helpful for vitiligo.8–10
Weak evidence suggests that phenylalanine may be helpful for multiple sclerosis when combined with transcutaneous electrical nerve stimulation (TENS).11
Very preliminary evidence suggests phenylalanine may reduce symptoms of Parkinson's disease (see Safety Issues below).12
Although it is sometimes proposed as a treatment for attention deficit disorder, phenylalanine taken alone does not appear to be helpful.13,14 Some proponents claim that it works better when combined with tyrosine, glutamine, and gamma-aminobutyric acid (GABA), but this has not been proven.
What Is the Scientific Evidence for Phenylalanine?
Depression
A pair of double-blind studies have found that D- or DL-phenylalanine is as effective as imipramine, a standard antidepressant drug, and that it may take effect much more quickly. The larger of the two studiescompared the effectiveness of D-phenylalanine at 100 mg daily against the same daily dose of imipramine.15 Sixty people with depression were randomly assigned to take either imipramine or D-phenylalanine for 30 days. The results in both groups were statistically equivalent, meaning that phenylalanine was about as effective as imipramine. D-phenylalanine worked more rapidly, however, producing significant improvement in only 15 days. Like most antidepressant drugs, imipramine required several weeks to take effect.
The other double-blind study followed 27 individuals, half of whom received DL-phenylalanine (150 to 200 mg daily) and the other half imipramine (100 to 150 mg daily).16 When they were reevaluated after 30 days, both groups had improved by a statistically equal amount. Very preliminary studies have also found benefits with L-phenylalanine.17,18
Unfortunately, there have been no good studies comparing any form of phenylalanine against placebo. This is too bad, since without such evidence we can't be sure that the supplement is actually effective.
Chronic Pain
The use of D-phenylalanine to treat pain is primarily based on a study involving 43 individuals with chronic pain, mostly due to arthritis.19 However, this was not a double-blind study, and it suffered from other flaws as well.20
A small double-blind study reportedly found evidence for the effectiveness of D-phenylalanine in chronic pain,21 but a careful look at the math involved undermined that conclusion.22 Another small study found no benefits.23
Safety Issues
The long-term safety of phenylalanine in any of its forms is not known. Both L- and D-phenylalanine must be avoided by those with the rare metabolic disease phenylketonuria (PKU).
The maximum safe dosages of phenylalanine have not been established for young children, pregnant or nursing women, or those with severe liver or kidney disease.
There are some indications that the combined use of phenylalanine with antipsychotic drugs might increase the risk of developing the long-term side effect known as tardive dyskinesia, or worsen symptoms in those who already have it.24,25,26
Like other amino acids, phenylalanine may interfere with the absorption or action of the drug levodopa which is used for Parkinson's disease.27
Interactions You Should Know About
If you are taking
View References
Last reviewed March 2002 by Medical Review Board
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