Theanine is an amino acid commonly found in tea. Theanine is related to a glutamine, and can cross the blood-brain barrier. Because it can enter the brain, theanine has psychoactive properties. Theanine has been shown to reduce mental and physical stress and can produce feelings of relaxation and anxiolysis.
Theanine is speculated to produce these effects by increasing the level of gamma-aminobutyric acid (GABA) production. Theanine increases brain serotonin, dopamine,
GABA levels and has micromolar affinities for AMPA, Kainate and NMDA receptors. Researchers also speculate that it may inhibit glutamic acid excitotoxicity. Theanine also promotes alpha wave production in the brain. It is theorized that the GABA-binding properties of theanine reduce the caffeine buzz delivered in black tea versus that of coffee.
