L-Theanine is the major amino acid found in Camellia sinensis, the source of green tea. It is an analog of the excitatory neurotransmitter, glutamate, and thusly, binds to glutamate receptors. L-Theanine can antagonize various glutamate receptor subtypes as well as inhibit glutamine and glutamate transporters, which has been shown to be neuroprotective in animal models of focal cerebral ischemia. Further, L-theanine is reported to increase brain levels of dopamine, serotonin, GABA, nerve growth factor, and brain-derived neurotrophic factor.

Green tea, oolong tea, black tea and other types of tea made from tea leaves often contain theanine, and one of the characteristics of high grade tea such as "Yulu" is that the content of theanine is especially high. The main effects and functions of L-Theanine are:

1.the effect on the central nervous system: Yokohoshi et al. in the determination of the effect of theanine on the metabolism of monoamines in various parts of the brain found that theanine can significantly promote the release of dopamine in the brain center and improve the physiological activity of dopamine in the brain. Dopamine is a central neurotransmitter that activates brain nerve cells, and its physiological activity is closely related to a person's emotional state.

2.antihypertensive effect: It is generally believed that the regulation of human blood pressure is influenced by the secretion of central and peripheral neurotransmitters catecholamines and 5-hydroxytryptamine. Studies have proved that theanine can effectively reduce spontaneous hypertension in rats. The hypertension-lowering effect shown by theanine can also be considered as a tranquilizing effect to some extent. And this stabilizing effect will undoubtedly help the recovery of physical and mental fatigue.

3.enhance memory, improve learning ability: theanine is a free amino acid unique to tea. The sweet taste of tea is brought by it. Theanine is most abundant in new tea and decreases with the fermentation process. It has been found that theanine can significantly promote the release of central dopamine in the brain and improve the physiological activity of dopamine in the brain. Therefore it can make people mentally happy, and at the same time will enhance memory and improve learning ability.

4.calm emotions, relieve physical and mental fatigue: theanine can activate the inhibitory nerves of the brain and sedate the excitatory nerves, which can improve sleep conditions and induce a sound sleep. By taking theanine at different times, the balance between wakefulness and sleepiness can be adjusted and kept at the appropriate level; theanine will play a hypnotic role at night and a waking role during the day.

5.Protection of nerve cells: theanine can inhibit the death of nerve cells caused by transient cerebral ischemia, and has a protective effect on nerve cells. The death of nerve cells is closely related to the excitatory neurotransmitter glutamate. Cell death occurs in the case of excess glutamate, which is usually the cause of Alzheimer's disease and other disorders.