L-Phenylalanine May Improve Mood

Phenylalanine is a unique amino acid and one of the few amino acids with both the L- and D- forms active. Because it serves as a precursor to the neurotransmitters involved in the elevation of mood, this amino acid supplement has been investigated for its antidepressant effects.

Phenylalanine is an essential, alpha amino acid. There are 3 forms of the amino acid: the natural L-phenylalanine, the synthetic try-phenylalanine-for-depression-and-anxiety, and DL-phenylalanine, a combination of the first two forms.

The primary use of L-phenylalanine in the body is in the production of tyrosine, another amino acid.

Tyrosine is the precursor of monoamine neurotransmitters such as dopamine, epinephrine, and norepinephrine. Given the importance of these brain chemicals, phenylalanine is important to maintain adequate levels of monoamine neurotransmitters in the brain.

When L-phenylalanine crosses into the brain, it is converted to L-tyrosine and then to L-dopa which is further converted into the three neurotransmitters mentioned above.

However, to cross the blood-brain barrier, L-phenylalanine shares the same transport mechanism with tryptophan.

Tryptophan is another amino acid essential for the synthesis of serotonin, a neurotransmitter important to mood. When phenylalanine is ingested in large amounts, it can reduce the absorption of tryptophan into the brain and, by extension, reduce the production of serotonin.

On the other hand, phenylalanine deficiency can cause mental confusion, reduced alertness, lethargy, depression, memory impairment and loss of appetite.

Overall, L-phenylalanine is the more active form of the amino acid in the brain because it crosses the blood-brain barrier more easily than the D-form.

At high doses, L-phenylalanine can actually serve as both an analgesic and an antidepressant. It achieves this feat by blocking a subgroup of calcium channels in the brain.

Other effects of L-phenylalanine in the brain include the antagonism of glycine and glutamate at specific receptors in the cortex and hippocampus. This antagonism of inhibitory neurotransmitters can also contribute to the antidepressant effect of the amino acid.

Although researchers have used doses as high as 2,500 mg/day of L-phenylalanine, such high doses are not recommended for long-term use unless recommended by a physician.

In treating depression, the usual recommended dose of DL-phenylalanine supplement is 100 – 200 mg/day.

Phenylalanine supplement should not be taken with meals with high protein content. This is because the absorption of phenylalanine will be reduced when more amino acids are present and competing for absorption sites.

This is all the more important at the blood-brain barrier. Since phenylalanine shares the same transport mechanism with other amino acids such as tryptophan, crossing into the brain becomes even more difficult when the concentrations of these competing amino acids are high.