Common Names

  • Theanine
  • Gamma-glutamylethylamide
  • N-ethylglutamic acid

For Patients & Caregivers

How It Works

L-theanine has not been shown to treat or prevent cancer.

L-theanine is an amino acid found in green tea. An epidemiological study showed that the incidence of stroke was reduced in individuals who consumed green tea. However, it is unclear whether L-theanine contributed to this benefit.

Laboratory and animal studies showed that L-theanine increases efficiency of chemotherapy drugs and also reduces their side effects. However, patients undergoing chemotherapy should discuss the use of L-theanine with their physicians because these effects are not based on clinical trials, and another component found in green tea called epigallocatechin-3-gallate (EGCG) reduces activity of the chemotherapy drug bortezomib.

Purported Uses
  • Relaxant
    In patients with schizophrenia, two studies have shown that L-theanine alleviates anxiety, and improves sleep and other related symptoms when combined with antipsychotic treatment.
  • 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 ADHD.
Patient Warnings

Although there are no reported side effects from taking L-theanine, consumption of large amounts of green tea can cause nausea, irritability, and GI upset because of its caffeine content.

Side Effects

Please see monograph on green tea.

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For Healthcare Professionals

Clinical Summary

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), antiobesity (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 alleviated anxiety and other related symptoms, and improved sleep in patients with schizophrenia (17) (21). In an open-label study of patients with major depressive disorder, L-theanine was safe and improved depressive symptoms, anxiety, sleep disturbance, and cognitive impairments (29).

Epidemiological data suggest its benefits with green tea for prevention of stroke (4), but it is unclear whether L-theanine contributed to this benefit. Small studies indicate that a combination of L-theanine and caffeine improves cognitive performance (14) (15), although behavior improvements observed with caffeine alone were lost with concomitant caffeine and L-theanine supplementation (22). L-theanine may help improve sleep quality in boys with attention deficit hyperactivity disorder (ADHD) (18).

Theanine derivatives are currently being studied in models of human and mouse cancers for their inhibitory effects (23).

L-theanine enhances the chemotherapeutic effects of doxorubicin (5) and idarubicin (6), and alleviates adverse effects from use of these agents both in vitro and in animal models (7) (24). However, patients undergoing chemotherapy should discuss the use of L-theanine with their physicians because these effects are not based on clinical trials, and epigallocatechin-3-gallate (EGCG) in green tea reduces activity of the chemotherapy drug bortezomib.

Food Sources

Green tea

Purported Uses
  • Cancer prevention
  • Cancer treatment
  • Relaxation
  • Stroke
Mechanism of Action

As a non-protein amino acid, L-theanine crosses the blood-brain barrier, exerting various neurophysiological and pharmacological effects including: anxiolytic and calming effects, due to inhibitory neurotransmitters and selective serotonin and dopamine modulation; cognitive improvements perhaps through decreased NMDA-dependent CA1 long-term potentiation (LTP) and increased NMDA-independent CA1-LTP; and improved selective attention during mental tasks likely due to changes in alpha brain wave activity (25). Neuroprotective effects are also thought to be due to its selective binding to glutamate receptors (2).

In animal models, L-theanine appears to have a dose-dependent biphasic effect on NSAID-induced gastric ulcers, delaying healing at higher doses (40 mg/kg), but accelerating healing at lower doses (10 mg/kg) perhaps through the maintenance of glutathione levels thus protecting against oxidative damage (26).

In human studies, L-theanine attenuated effects of caffeine on oxygenated hemoglobin, cognition, and mood, suggesting both independent and interactive effects between the two compounds (22). Other studies suggest that combining caffeine and theanine intake causes their individual effects to counteract each other (30) (31). L-theanine also stabilizes glutamatergic concentrations in the brain, which may explain its therapeutic effect in patients with schizophrenia (21).

L-theanine was shown 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, hence attenuating effects of these drugs. Consequent mechanistic studies revealed that L-theanine, a glutamate analogue, competes with glutamate to bind the glutamate receptor, resulting in suppression of chemotherapy efflux (extracellular transport), increasing their concentration (27).

Interestingly, L-theanine also reduces the adverse effects of doxorubicin. The proposed mechanism is based on the variance of glutamate receptors expressed in normal and tumor cells. Whereas theanine binds the glutamate receptor in tumor cells, it is metabolized to glutamate in normal cells. This increase in glutamate likely results in increased efflux of doxorubicin from the cells, thereby decreasing toxicity (28).

Animal models indicate the prevention of doxorubicin-induced acute hepatotoxicity occurs through suppression of intrinsic caspase-3-dependent apoptotic signaling (24). L-theanine does not induce or inhibit cytochrome P450 enzymes (9).

Some novel theanine derivatives were found to inhibit lung tumor growth by targeting EGFR/VEGFR-Akt/NF-kappaB pathways (23).


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
  • Sedatives
Adverse Reactions

Please see monograph on Green Tea.

Herb-Drug Interactions
  • Midazolam: L-theanine may have additive effects (19).
Dosage (OneMSK Only)
  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. 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.

  8. Ota M, Wakabayashi C, Sato N, et al. Effect of l-theanine on glutamatergic function in patients with schizophrenia. Acta Neuropsychiatr. Apr 21 2015:1-6.

  9. Nagai K, Oda A, Konishi H. Theanine prevents doxorubicin-induced acute hepatotoxicity by reducing intrinsic apoptotic response. Food Chem Toxicol. Apr 2015;78:147-152.

  10. Chatterjee S, Chatterjee A, Roy S, et al. L-Theanine healed NSAID-induced gastric ulcer by modulating pro/antioxidant balance in gastric ulcer margin. J Nat Med. Oct 2014;68(4):699-708.

  11. Sugiyama T, Sadzuka Y, Tanaka K, et al. Inhibition of glutamate transporter by theanine enhances the therapeutic efficacy of doxorubicin. Toxicol Lett. Apr 30 2001;121(2):89-96.

  12. Hidese S, Ota M, Wakabayashi C, et al. Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study. Acta Neuropsychiatr. Apr 2017;29(2):72-79.

  13. Giles GE, Mahoney CR, Brunye TT, et al. Caffeine and theanine exert opposite effects on attention under emotional arousal. Can J Physiol Pharmacol. Jan 2017;95(1):93-100.

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