NOW L-Phenylalanine, 500mg, 120 caps

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.

L-phenylalanine crosses into the brain, it is converted to L-tyrosine and then to L-dopa. 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. A phenylalanine deficiency can cause mental confusion, reduced alertness, lethargy, depression, memory impairment and loss of appetite.

 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. These antagonism of inhibitory neurotransmitters can also contribute to the antidepressant effect of the amino acid.