Phenylalanine is a ringed amino acid that is readily available in most food sources, particularly meats and milk products, with lower levels found in oats and wheat germ. It is essential for many bodily functions and is one of the few amino acids that can cross the blood-brain barrier and thus directly affect brain chemistry. Phenylalanine is the precursor of the amino acid tyrosine, which cannot be reconverted, so phenylalanine is essential in the diet. As a precursor of tyrosine, phenylalanine can form norepinephrine in the brain in addition to other catecholamines such as epinephrine, dopamine, and tyramine. Norepinephrine is an important neurotransmitter (that is, it conveys chemoelectric information at nerve synapses) and is apparently important for memory, alertness, and learning. Phenylalanine metabolism requires pyridoxine (B6), niacin (B3), vitamin C, copper, and iron. This amino acid is part of some psychoactive drugs as well as body chemicals such as acetylcholine, melanotropin, vasopressin, cholecystokinins, and the enkephalins and endorphins.
Phenylalanine has been used for treatment of depression in the D-, L-, or DL- forms, probably because it forms tyrosine, an excitatory neurotransmitter. Braverman and Pfeiffer, in The Healing Nutrients Within, suggest that L-phenylalanine works best in bipolar disorders (with manic and depressive states) in doses of 500 mg. twice daily up to 2–3 grams daily, along with 100 mg. of vitamin B6 twice daily, whereas D- and DL-phenylalanine work better for affective (lack of positive attitude or emotional enthusiasm for life) depression. Phenylalanine is better absorbed than tyrosine and produces fewer headaches, so may be more useful in depression than L-tyrosine. Both DL- and D-phenylalanine are helpful pain relievers in certain musculoskeletal problems, and this is their primary use currently. Aspartame, the new nutrient sweetener, is synthesized from the combination of aspartic acid and phenylalanine. Aspartame is safe, except for pregnant women or people with phenylketonuria (PKU), a genetic problem of phenylalanine metabolism.
I have used phenylalanine in particular for patients with pain problems, most commonly back pain due to muscular or ligamentous irritation, though it may be helpful for any type of pain. It probably works for this purpose because of its function of increasing endorphins in the brain, but it is not really a treatment for the cause of the pain, such as inflammation or spasms. The endorphins are thought to give us a more positive outlook on life, to enhance alertness, and to improve vitality. (This may be a reason why phenylalanine works for depression.) Endorphins are the mysterious substances released when we exercise or when we experience positive emotions. They are also thought to make us less sensitive to or aware of pain. DL-phenylalanine blocks the enkephalinase enzymes that break down the endorphins and enkephalins, the natural pain relievers and mood elevators. However, this substance does not work all the time, nor is it a complete therapy; the underlying cause of the pain or depression should be discovered.
Some of the pain problems for which phenylalanine may be helpful are low back pain; neck pain; osteoarthritis; rheumatoid arthritis; menstrual cramps; and headaches, particularly migraines. However, patients suffering from migraines may have elevated phenylalanine levels, in which case supplementation would not help. L-tryptophan may work better in these patients.
On a trial basis, to see whether it will be helpful for pain, DL-phenylalanine can be taken in a dose of about 500–750 mg. two to three times daily. It really has no common side effects other than occasional headache or jitteriness. However, its catecholamine effect may raise blood pressure in some people, so this should be watched. Phenylalanine therapy is not recommended for long-term use; as with the other amino acids, it should not be taken for more than three weeks at a time without a break or without the support of the other amino acids.