Nonessential Micronutrient



Phenylalanine in the form of L-phenylalanine may help relieve stress, elevate mood, aid in memory, and suppress appetite, while the D-phenylalanine form appears to act mostly as a pain reliever.

Other names for Phenylalanine

L-phenylalanine, D-phenylalanine

Where to find Phenylalanine

L-Phenylalanine is found in most protein-rich foods.

D-Phenylalanine is not found in food sources and is made synthetically.


Why athletes use Phenylalanine

Athletes use phenylalanine for improved focus during workouts, to help relieve post-exercise soreness, and as an occasional appetite suppressant. It is also used to improve memory and lift depression.

Ways that Phenylalanine can enhance Fat Loss:
  • Suppress appetite to support weight loss
Ways that Phenylalanine can enhance Mental Functioning:
  • Improve focus and mental alertness as well as memory


Signs of Phenylalanine deficiency

No deficiency conditions are known to exist.

Potential uses for Phenylalanine

Research indicates that Phenylalanine may be useful in the treatment of:

  • Depression
  • Bipolar disorder (manic depression)
  • ALS


More about Phenylalanine

Phenylalanine is an essential amino acid that comes in three distinct forms — the L form; its mirror image, the D form; and a 50/50 combination of the two that’s known as DLPA. The L form and D form have very different effects on the body, and DLPA is believed to be the “best of both worlds,” so to speak.

L-Phenylalanine — the mood elevator

The most common form, L-phenylalanine, is converted into the amino acid tyrosine in the body through some complex chemical reactions in the liver. L-Tyrosine, in turn, is a brain messenger that can be converted into dopamine and norepinephrine. Through these conversions, L-phenylalanine may be able to help relieve stress and depression, elevate mood and vitality, aid in memory and learning, relieve symptoms of bipolar disorder, as well as helping suppress appetite. And, of course, it is one of the building blocks of proteins, as are all amino acids.

Phenylalanine has also been shown to increase the concentrations of a chemical messenger in the brain known for its importance in generating romantic feelings and increasing libido — phenylethylamine. Research has shown that individuals who have become disinterested in sex appear to have low levels of phenylethylamine in their brains.

D-Phenylalanine — the pain reliever

Interestingly, D-phenylalanine also has effects in the body. This is unusual because the D form of this amino acid is not “found in nature.” As well, it has significantly different effects than the L form, appearing to act mostly as a potent pain reliever by inhibiting the enzymes that break down some of the body’s own natural pain killers.

The pain-blocking effects of D-phenylalanine have been shown to actually grow stronger with time. This is opposite of the usual effect of most pain fighters, which become less effective as the body grows used to them. In addition, D-phenylalanine apparently works well with pain medications, making them stronger. It has been shown to be helpful in treating Parkinson’s disease, alleviating the symptoms of premenstrual syndrome, and the relief of chronic pain.

In conclusion

This amazing amino acid appears to have a wide variety of effects for all types of active people. Experiencing pain from an injury or overexertion? Dive for the D form. Feeling lack of focus or too much stress? Leap for the L form. Either way, phenylalanine appears to be a safe, effective tool to add to your training toolbox.

For more information on DLPA and how it may be used, click here.



200 to 1,500 mg is typically taken per day. Some experts suggest that more is needed for pain relief and to reduce depression (up to the 1,500 mg amount).

While levels up to 4 grams have been used under clinical supervision, lower levels have produced similar results.


Phenylalanine is taken on an empty stomach once or twice a day. To reduce appetite, phenylalanine should be taken one hour before meals. Because phenylalanine competes with other amino acids, it is not recommended to be supplemented with protein foods.

To avoid becoming over-stimulated, do not take phenylalanine before bed.

Synergists of Phenylalanine

Vitamins B3, B6, and C may enhance the effects of phenylalanine, especially when tyrosine is also supplemented.

Copper and iron may enhance the effects of phenylalanine.

Safety of Phenylalanine

Cancer patients, especially those with skin cancer, should not supplement with phenylalanine, as some cancers use this amino acid to fuel their growth.

If you are pregnant or lactating, phenylalanine is not recommended.

As it may have stimulating effects, it is not recommended for people who suffer from anxiety attacks.

Do not use if you have phenylketonuria (PKU).

Because phenylalanine has been shown to raise blood pressure, it is not recommended for people with high blood pressure or heart conditions.

Drugs that interact with Phenylalanine

Do not use if using antidepressants or other MAO inhibitors.

Toxicity of Phenylalanine

Over 1,500 mg per day is not recommended unless under the supervision of a physician.

Bans and restrictions

None reported.


  • Budd, K., “Use of D-Phenylalanine, an Enkephalinase Inhibitor, in the Treatment of Intractable Pain,” Adv Pain Res Ther 5 (1983) : 305-8.
  • Holt, S. “Natural Approaches to Promote Sexual Function,” Alt & Comp Therapies 8 (1999) : 204-8.
  • Holt, S. The Sexual Revolution (Fairfield, NJ: BTI Publishing, 1999).
  • Fischer, E, et al., “Therapy of Depression by Phenylalanine,” Arzneimittelforschung 25.1 (1975) :132.
  • Heller, B., et al., “Therapeutic Action of D-Phenylalanine in Parkinson’s Disease,” Arzneimittelforschung 26.4 (1976) : 577-9.
  • Sabelli, H.C., et al., “Clinical Studies on the Phenylethylamine Hypothesis of Affective Dissorder: Urine and Blood Phenylacetic Acid and Phenylalanine Dietary Supplements,” J Clin Psychiatry 47.2 (1986) : 66-70.