L-Theanine

L-Theanine

L-Theanine

Common Names

  • Theanine
  • gamma-glutamylethylamide

For Patients & Caregivers

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.

  • Relaxant
    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.
  • Stroke
    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.

Please see monograph on Green tea.

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For Healthcare Professionals

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).

Green tea

  • Cancer prevention
  • Cancer treatment
  • Relaxation
  • Stroke

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
  • Sedatives

Please see monograph on Green Tea.

  • Midazolam: L-theanine may have additive effects (19).

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.
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.


  1. 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.

  2. 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.

  3. 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.

  4. Yokogoshi H, et al. Theanine-induced reduction of brain serotonin concentration in rats. Biosci Biotechnol Biochem 1998; 62(4): 816-17.

  5. 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.

  6. 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.

  7. Zarse K, Jabin S, Ristow M. L-Theanine extends lifespan of adult Caenorhabditis elegans. Eur J Nutr. 2012 Sep;51(6):765-8.

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