Health Care Professional Information
L-theanine is a water soluble amino acid found in green tea and in mushrooms. Purified L-theanine is available as an oral dietary supplement. It is consumed for its perceived antioxidant and relaxant effects (12). Several in vitro and animal studies have shown that L-theanine has lipid lowering (1), neuroprotective (2) (16), anti-obesity (3) and antitumor (1) properties. It can also affect the levels of some neurotransmitters (10) (11), prevent beta-amyloid-induced cognitive dysfunction (13), and was shown to extend longevity in C. elegans (20).
When combined with antipsychotic treatment, L-theanine was shown to alleviate anxiety in patients with schizophrenia (17). Epidemiological data suggest its benefits for prevention of stroke (4) and small studies indicate that a combination of L-theanine and caffeine improves cognitive performance (14) (15). L-theanine may help improve sleep quality in boys with attention deficit hyperactivity disorder (ADHD) (18).
L-theanine also enhances the chemotherapeutic effects of doxorubicin (5) and idarubicin (6), and alleviates the adverse effects from use of these agents in vitro (7).
- Cancer prevention
- Cancer treatment
Mechanism of Action
L-theanine is thought to increase the antitumor activity of chemotherapeutic drugs, doxorubicin and idarubicin (5) (6). These agents normally bind the glutamate receptor and the complex is transported across the cell resulting in reduced concentrations and hence attenuated effects of these drugs. L-theanine competes with chemo drugs for binding the glutamate receptor and prevents their efflux. It was also shown to affect levels of dopamine and serotonin in animals (10) (11). The neuroprotective effects of L-theanine are also thought to be due to its selective binding to glutamate receptors (2). L-theanine does not induce or inhibit cytochrome P450 enzymes (9).
Studies in rats have demonstrated that it is absorbed into plasma and tissues, and reaches a maximum level at 0.5 - 2 hrs following oral absorption. It is believed that L-theanine is hydrolyzed in the kidneys to glutamic acid and ethylamine by phosphate-independent glutaminase. The byproducts are eliminated from the body within 24 hrs (2) (8).
Although there are no reported side effects from taking L-theanine, consumption of large amount of green tea can cause nausea, irritability, and GI upset because of the caffeine content.
- Hypersensitivity to green tea
- Pregnancy and lactation
- Chemotherapeutic drugs
- Lipid lowering drugs
- Midazolam: L-theanine may have additive effects (19).
Literature Summary and Critique
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- Zhang G, Miura Y, Yagasaki K. Effects of dietary powdered green tea and L-theanine on tumor growth and endogenous hyperlipidemia in hepatoma-bearing rats. Biosci Biotechnol Biochem. 2002; 66(4):711-6.
- Kakuda T. Neuroprotective effects of the green tea components L-theanine and catechins. Biol Pharm Bull. 2002; 25(12):1513-8.
- Zheng G, Sayama K, Okubo T, Juneja LR, Oguni I. Anti-obesity effects of three major components of green tea, catechins, caffeine and L-theanine, in mice. In Vivo. 2004;18(1):55-62.
- Sato Y, Nakatsuka H, Watanabe T, Hisamichi S, Shimizu H, Fujisaku S, et al. Possible contribution of green tea drinking habits to the prevention of stroke. Tohoku J Exp Med. 1989; 157(4):337-43.
- Sugiyama T, Sadzuka Y. Combination of L-theanine with doxorubicin inhibits hepatic metastasis of M5076 ovarian sarcoma. Clin Cancer Res. 1999; 5(2):413-6.
- Sadzuka Y, Sugiyama T, Sonobe T. Improvement of idarubicin induced antitumor activity and bone marrow suppression by L-theanine, a component of tea. Cancer Lett. 2000;158(2):119-24.
- Sugiyama T, Sadzuka Y. L-theanine, a specific glutamate derivative in green tea, reduces the adverse reactions of doxorubicin by changing the glutathione level. Cancer Lett. 2004;212(2):177-84.
- Tsuge H, Sano S, Hayakawa T, Kakuda T, Unno. T. L-theanine, gamma-glutamylethylamide, is metabolized by renal phosphate-independent glutaminase. Biochim Biophys Acta. 2003;1620(1-3):47-53.
- Sadzuka Y, et al. Efficacy of theanine is connected with theanine metabolism by any enzyme, not only drug metabolizing enzymes. Food Chem Toxicol 2006; 44(2):286-92.
- Yokogoshi H, et al. Theanine-induced reduction of brain serotonin concentration in rats. Biosci Biotechnol Biochem 1998; 62(4): 816-17.
- Yokogoshi H, et al. Effect of theanine, r-glutamylethylamide, on brain monoamines and striatal dopamine release in conscious rats. Neurochem Res 1998; 23(5): 667-73.
- Lu K, et al. The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans. Hum Psychopharmacol Clin Exp 2004: 19: 457-65.
- Kim TI, Lee YK, Park SG, et al. l-Theanine, an amino acid in green tea, attenuates beta-amyloid-induced cognitive dysfunction and neurotoxicity: reduction in oxidative damage and inactivation of ERK/p38 kinase and NF-kappaB pathways. Free Radic Biol Med. 2009 Dec 1;47(11):1601-10.
- Owen GN, Parnell H, De Bruin EA, Rycroft JA. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci. 2008 Aug;11(4):193-8.
- Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci. 2010 Dec;13(6):283-90.
- Di X, Yan J, Zhao Y, et al. L-theanine protects the APP (Swedish mutation) transgenic SH-SY5Y cell against glutamate-induced excitotoxicity via inhibition of the NMDA receptor pathway. Neuroscience. 2010 Jul 14;168(3):778-86.
- Ritsner MS, Miodownik C, Ratner Y, et al. L-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder: an 8-week, randomized, double-blind, placebo-controlled, 2-center study. J Clin Psychiatry. 2011 Jan;72(1):34-42.
- Lyon MR, Kapoor MP, Juneja LR. The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Altern Med Rev. 2011 Dec;16(4):348-54.
- Heese T, Jenkinson J, Love C, et al. Anxiolytic effects of L-theanine—a component of green tea—when combined with midazolam, in the male Sprague-Dawley rat. AANA J. 2009 Dec;77(6):445-9.
- Zarse K, Jabin S, Ristow M. L-Theanine extends lifespan of adult Caenorhabditis elegans. Eur J Nutr. 2012 Sep;51(6):765-8.
How It Works
Bottom Line: L-theanine has not been shown to treat or prevent cancer.
L-theanine is an amino acid found in green tea. Laboratory and animal studies showed that L-theanine increases efficiency of chemo drugs and also reduces side effects from use of such drugs. An epidemiological study showed that green tea reduced the incidence of stroke in individuals who consumed green tea. However, it is unclear if L-theanine contributed to this benefit.
Animal studies have shown that L-theanine has relaxant properties but it does not reduce anxiety.
- Cancer prevention
There is no scientific evidence to substantiate this use.
- Cancer treatment
Laboratory and animal studies indicate that L-theanine has antitumor properties but human data are lacking.
Results from a study done in Japan suggest that green tea consumption decreased the risk of stroke in individuals. However, it is unclear if L-theanine contributed to this benefit.
- Attention deficit hyperactivity disorder (ADHD)
A small study suggests L-theanine can improve sleep quality in boys with attention deficit hyperactivity disorder.
Attention deficit hyperactivity disorder (ADHD):
This study involved 98 boys, ages 8-12 years, previously diagnosed with ADHD. Subjects were randomized to receive two chewable tablets twice daily (at breakfast and after school), each tablet containing 100 mg of L-theanine, or placebo for six weeks. They were evaluated for five consecutive nights using wrist actigraphy at baseline, and again at the end of the treatment period. The Pediatric Sleep Questionnaire (PSQ) was completed by parents at baseline and at the end of the treatment period. Boys in the L-theanine group had significantly higher sleep percentage and sleep efficiency scores compared to those in the placebo group. L-theanine was tolerated well with no significant adverse effects.
Although there are no reported side effects from taking L-theanine, consumption of large amount of green tea can cause nausea, irritability, and GI upset because of its caffeine content.
Last updated: March 19, 2014