|Systematic (IUPAC) name|
|Mol. mass||174.20 g/mol|
|Melt. point||117 °C (243 °F)|
Theanine is an amino acid commonly found in tea (infusions of Camellia sinensis). Theanine is related to 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 may produce feelings of relaxation.
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. It has also been found that injecting spontaneously hypertensive mice with theanine significantly lowered levels of 5-hydroxyindole in the brain. Researchers also speculate that it may inhibit glutamic acid excitotoxicity. Theanine also promotes alpha wave production in the brain.
Studies on test rats have shown that even repeated, extremely high doses of theanine cause little to no harmful psychological or physical effects.
L-theanine may help the body's immune system response when fighting infection by boosting the disease-fighting capacity of gamma delta T cells. The study, published in 2003 by the Brigham and Women's Hospital, included a four-week trial with 11 coffee drinkers and 10 tea drinkers, who consumed 600 milliliters of coffee or black tea daily. Blood sample analysis found that the production of anti-bacterial proteins was up to five times higher in the tea-drinkers, an indicator of a stronger immune response.
Recently, marketing campaigns from tea companies have been emphasizing the natural presence of L-theanine in their tea and that L-theanine boosts the production of alpha brainwaves. 
- Yokogoshi H, Kobayashi M, Mochizuki M, Terashima T (1998). "Effect of theanine, r-glutamylethylamide, on brain monoamines and striatal dopamine release in conscious rats". Neurochem Res. 23 (5): 667–73. PMID 9566605.
- Gomez-Ramirez M. "The Deployment of Intersensory Selective Attention: A High-density Electrical Mapping Study of the Effects of Theanine". Clin Neuropharmacol. 30 (1): 25–38. PMID 17272967.
- Kimura K, Ozeki M, Juneja L, Ohira H (2007). "L-Theanine reduces psychological and physiological stress responses". Biol Psychol. 74 (1): 39–45. PMID 16930802.
- Lu K, Gray M, Oliver C, Liley D, Harrison B, Bartholomeusz C, Phan K, Nathan P (2004). "The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans". Hum Psychopharmacol. 19 (7): 457–65. PMID 15378679.
- Nathan P, Lu K, Gray M, Oliver C (2006). "The neuropharmacology of L-theanine(N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent". J Herb Pharmacother. 6 (2): 21–30. PMID 17182482.
- Yokogoshi H, Kato Y, Sagesaka YM, Takihara-Matsuura T, Kakuda T, Takeuchi N (1995). "Reduction effect of theanine on blood pressure and brain 5-hydroxyindoles in spontaneously hypertensive rats.". Biosci Biotechnol Biochem. 59 (4): 615–618. PMID 7539642.
- Borzelleca J, Peters D, Hall W (2006). "A 13-week dietary toxicity and toxicokinetic study with L-theanine in rats". Food Chem Toxicol. 44 (7): 1158–66. PMID 16759779.
- Kamath A, Wang L, Das H, Li L, Reinhold V, Bukowski J (2003). "Antigens in tea-beverage prime human Vgamma 2Vdelta 2 T cells in vitro and in vivo for memory and nonmemory antibacterial cytokine responses". Proc Natl Acad Sci U S A. 100 (10): 6009–14. PMID 12719524.
- Lipton's L-theanine page