Phenylalanine
D-Phenylalanine; DL-Phenylalanine; L-Phenylalanine
Proposed Uses: Depression; Attention Deficit Disorder; Multiple Sclerosis; Parkinson's Disease; Pain; Rheumatoid Arthritis; Vitiligo
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, and a combination of the two known as DL-phenylalanine.
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.
Requirements/Sources
L-phenylalanine 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- and DL-phenylalanine are typically taken at a dose of 100 to 200 mg daily for the treatment of depression. For the treatment of chronic pain, studies have used D-phenylalanine in doses 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
Small double-blind comparative studies suggest that both the D- and DL- forms of phenylalanine might be helpful for depression.
Weak and contradictory evidence has been used to advocate the use of D-phenylalanine as a general pain relieving treatment.
Preliminary uncontrolled and double-blind studies found that L-phenylalanine may enhance the effectiveness of ultraviolet for vitiligo.
Highly preliminary evidence suggests that D-phenylalanine may be helpful for multiple sclerosis when combined with transcutaneous electrical nerve stimulation (TENS). D-phenylalanine has also been proposed as a treatment for Parkinson's disease.
Although D- and DL- phenylalanine are marketed as treatments for attention deficit disorder, they do not appear to be helpful. Some proponents claim that phenylalanine 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 comparative studies found that D- or DL-phenylalanine may be as effective as the antidepressant drug imipramine, and possibly work more quickly.
Unfortunately, there have not been any controlled studies of phenylalanine for depression. Without such evidence we can't be sure that the supplement is actually effective.
Chronic Pain
As yet there is no meaningful evidence that it really works. A study commonly described as showing D-phenylalanine effective suffered from many flaws (including the fact that it lacked a control group) and therefore can't be trusted.
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.
Like other amino acids, phenylalanine may interfere with the absorption or action of the drug levodopa which is used for Parkinson's disease.
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