L-Tyrosine is used in the body to make the catecholamines dopamine (DA) and norepinephrine (NE), which can become depleted under stressful or cognitively challenging conditions. After supplementation, L-tyrosine levels in the blood peak after one to two hours, and stay elevated for up to eight hours.[1] L-tyrosine then passes through the blood-brain barrier, where it is absorbed by brain cells and converted in a series of enzymatic reactions to DA, which can be converted to NE through the action of another enzyme.[2] The ability of L-tyrosine to enhance catecholamine synthesis only in neurons that are actively firing may explain its ability to reverse the effects of neurotransmitter depletion during stress.[3]
