L-Theanine is an amino acid found almost exclusively in tea that influences the central nervous system through a number of mechanisms. It crosses the blood-brain barrier in a dose-dependent manner within 30 minutes, and influences levels of the neurotransmitters dopamine, gamma-aminobutyric acid (GABA), serotonin, norepinephrine, and glutamate. These effects cause a significant increase in alpha brain wave activity, indicative of a state of wakeful relaxation, increased performance under stress, improved learning and concentration, as well as decreased anxiety.
Studies also suggest that L-theanine may have neuroprotective properties against brain injury, such as that resulting from stroke, as well as from environmental neurotoxins. L-Theanine‚„s neuroprotective capacity has been attributed to its effects on N-methyl-D-aspartate (NMDA) receptors, and brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) production. Because it reduces levels of norepinephrine, it has also been shown to have a hypotensive effect. In clinical trials, L-Theanine has been shown to buffer sympathetic activity during stressful events, reducing subjective as well as physiological stress responses.