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What do they do?
L-phenylalanine (LPA) serves as a building block for the various proteins that are produced in the body. LPA can be converted to L-tyrosine (another amino acid) and subsequently to L-dopa, norepinephrine, and epinephrine. LPA can also be converted (through a separate pathway) to phenylethylamine, a substance that occurs naturally in the brain and appears to elevate mood.

D-phenylalanine (DPA) is not normally found in the body and cannot be converted to L-tyrosine, L-dopa, or norepinephrine. As a result, DPA is converted primarily to phenylethylamine (the potential mood elevator). DPA also appears to influence certain chemicals in the brain that relate to pain sensation.

DLPA is a mixture of LPA and its mirror image DPA. DLPA (or the D- or L-form alone) has been used to treat depression.1 2 DPA may be helpful for some people with Parkinson’s disease3 and has been used to treat chronic pain—including pain from osteoarthritis and rheumatoid arthritis—with both positive4 and negative5 results. No research has evaluated the effectiveness of DLPA on rheumatoid arthritis.

Where are they found?
LPA is found in most foods that contain protein. DPA does not normally occur in food. However, when phenylalanine is synthesized in the laboratory, half appears in the L-form and the other half in the D-form. These two compounds can also be synthesized individually, but it is more expensive to do so. The combination supplement (DLPA) is often used because of the lower cost and because both components exert different health-enhancing effects.

Phenylalanine has been used in connection with the following conditions (refer to the individual health concern for complete information):


Rating Health Concerns

Depression (DPA, LPA, DLPA)
Low back pain (DPA)
Pain (DPA)
Parkinson’s disease (DPA)
Vitiligo (LPA)


Alcohol withdrawal support (DLPA)
Osteoarthritis (DPA)
Rheumatoid arthritis (DPA)

Reliable and relatively consistent scientific data showing a substantial health benefit.
Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.


Who is likely to be deficient of phenylalanine?

People whose diets are very low in protein may develop a deficiency of LPA, although this is believed to be very uncommon. However, one does not necessarily have to be deficient in LPA in order to benefit from a DLPA supplement.

How much phenylalanine is usually taken?

DLPA has been used in amounts ranging from 75–1,500 mg per day. This compound can have powerful effects on mood and on the nervous system, and therefore DLPA should be taken only under medical supervision. LPA has been used in amounts up to 3.5 grams per day. For best results, phenylalanine should be taken between meals, because the protein present in food can interfere with the uptake of phenylalanine into the brain, potentially reducing its effect.

Are there any side effects or interactions with phenylalanine?

The maximum amount of DLPA that is safe is unknown. However, consistent toxicity in healthy people has not been reported with 1,500 mg per day or less of DLPA, except for occasional nausea, heartburn, or transient headaches.

When 100 mg of LPA per 2.2 pounds body weight or more was given to animals, a variety of complex problems occurred, leading two researchers to have concerns about potential toxicity of high amounts in humans.6 While these concerns were directed at LPA specifically, they are likely to be equally applicable to DLPA. Although no serious adverse effects have been reported in humans taking phenylalanine, amounts greater than 1,500 mg per day should be supervised by a doctor.

People with phenylketonuria must not supplement with phenylalanine.

Some research suggests that people with tardive dyskinesia may process phenylalanine abnormally. Until more is known, it makes sense for people with this condition to avoid phenylalanine supplementation.

LPA competes with several other amino acids for uptake into the body and the brain. Therefore, for best results, phenylalanine should be taken between meals, or away from protein-containing foods. People taking prescription or over-the-counter medications should consult a physician before taking DLPA.

At the time of writing, there were no well-known drug interactions with phenylalanine.