Other Name(s):

2-Amino-4- (ethylcarbamoyl) Butyric Acid, 5-N-ethylglutamine, Gamma-glutamylethylamide, L-Theanine, L-Théanine, N-Éthyl-L-Glutamine, Teanina, Théanine.


Theanine is an amino acid found in green tea. It is also found in some mushrooms. It is similar in structure to glutamic acid, another amino acid.

People take theanine by mouth for reducing anxiety and stress, for preventing Alzheimer's disease, for treating attention deficit-hyperactivity disorder (ADHD), and improving mental performance and attention. Theanine is also used for reducing blood pressure, preventing the flu, and improving how well cancer drugs work.

How does it work?

Theanine has a chemical structure very similar to glutamate, a naturally occurring amino acid. Glutamate helps transmit nerve impulses in the brain. Some of the effects of theanine appear to be similar to glutamate, and some effects seem to block glutamate. Theanine may also affect some brain chemicals called GABA, dopamine, and serotonin.

Uses & Effectiveness

Possibly Effective for...

  • Mental performance. Early research shows that taking theanine before a test can reduce the rate of errors. Also, most research shows that taking theanine along with caffeine increases alertness and improves a person's ability to switch attention between different tasks.

Insufficient Evidence to Rate Effectiveness for...

  • Attention deficit hyperactivity disorder (ADHD). Early research shows that taking 200 mg of theanine (Suntheanine by Taiyo Kagaku) by mouth twice daily for 6 weeks increases restful sleep and decreases nightly activity during sleep in boys ages 8-12 diagnosed with ADHD.
  • Influenza (flu). Early research shows that taking a combination of green tea extract (THEA-FLAN 90S, Ito-en Co.) plus theanine (Suntheanine, Taiyo Kagaku) daily for 5 months may lower the risk of developing the flu.
  • Stress. The effects of theanine on stress are conflicting. Some early research shows that taking 200 mg of theanine before an exam reduces anxiety and may prevent blood pressure from increasing due to stress. Other early research shows that taking 200 mg of theanine twice daily before and during pharmacy practice decreases stress levels. However, another early study shows that taking 200 mg of theanine helps promote tranquility in people who are already relaxed. But it doesn't work in people who are stressed. Reasons for the conflicting results are not clear.
  • Other conditions.
More evidence is needed to rate the effectiveness of theanine for these uses.

Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, and Insufficient Evidence to Rate (detailed description of each of the ratings).


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Side Effects

Theanine is POSSIBLY SAFE when used by mouth, short-term. Doses of up to 250 mg of theanine have been safely used one time per week for 3 weeks. Also, a specific combination product containing theanine and other green tea ingredients has also been used safely when taken once daily for up to 5 months. It is not known if theanine is safe when used for longer periods of time. Theanine may cause mild adverse effects, such as headache.

Special Precautions & Warnings

Pregnancy and breast-feeding:There is not enough reliable information about the safety of using theanine if you are pregnant or breast-feeding. Stay on the safe side and avoid use.

Children: Theanine is POSSIBLY SAFE for children. Doses of 200 mg of theanine have been safely used twice daily for up to 6 weeks.

Low blood pressure: Theanine might lower blood pressure. In theory, theanine might increase the risk of blood pressure dropping too low in people prone to low blood pressure. If you have low blood pressure, discuss theanine with your healthcare provider before starting it.


Medications for high blood pressure (Antihypertensive drugs)Interaction Rating: Moderate Be cautious with this combination.Talk with your health provider.

Theanine might decrease blood pressure. Taking theanine along with medications for high blood pressure might cause your blood pressure to go too low.

Some medications for high blood pressure include captopril (Capoten), enalapril (Vasotec), losartan (Cozaar), valsartan (Diovan), diltiazem (Cardizem), Amlodipine (Norvasc), hydrochlorothiazide (HydroDiuril), furosemide (Lasix), and many others.

Stimulant drugsInteraction Rating: Moderate Be cautious with this combination.Talk with your health provider.

Stimulant drugs speed up the nervous system. By speeding up the nervous system stimulant medications can make you feel jittery and speed up your heartbeat. Theanine might work to slow down the nervous system. Taking theanine along with stimulant medications might decrease the effectiveness of stimulant medications.

Some stimulant drugs include diethylpropion (Tenuate), epinephrine, phentermine (Ionamin), pseudoephedrine (Sudafed), and many others.


Next to red peppers, you can get the most vitamin C from ________________. See Answer



  • Mental performance: A single dose of 100 mg of theanine before a test has been used (91747). Theanine has also been used in combination with caffeine. Combination doses have ranged from 30-100 mg of caffeine and 12-100 mg of theanine.

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Reviewed on 6/14/2021

Egashira, N., Ishigami, N., Pu, F., Mishima, K., Iwasaki, K., Orito, K., Oishi, R., and Fujiwara, M. Theanine prevents memory impairment induced by repeated cerebral ischemia in rats. Phytother.Res 2008;22(1):65-68. View abstract.

Giesbrecht, T., Rycroft, J. A., Rowson, M. J., and De Bruin, E. A. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci. 2010;13(6):283-290. View abstract.

Haskell, C. F., Kennedy, D. O., Milne, A. L., Wesnes, K. A., and Scholey, A. B. The effects of L-theanine, caffeine and their combination on cognition and mood. Biol.Psychol. 2008;77(2):113-122. View abstract.

Kakuda, T. Neuroprotective effects of the green tea components theanine and catechins. Biol Pharm Bull 2002;25(12):1513-1518. View abstract.

Kakuda, T., Nozawa, A., Sugimoto, A., and Niino, H. Inhibition by theanine of binding of [3H]AMPA, [3H]kainate, and [3H]MDL 105,519 to glutamate receptors. Biosci.Biotechnol.Biochem. 2002;66(12):2683-2686. View abstract.

Kamath, A. B., Wang, L., Das, H., Li, L., Reinhold, V. N., and Bukowski, J. F. 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 5-13-2003;100(10):6009-6014. View abstract.

Kimura, K., Ozeki, M., Juneja, L. R., and Ohira, H. L-Theanine reduces psychological and physiological stress responses. Biol Psychol. 2007;74(1):39-45. View abstract.

Matsumoto, K., Yamada, H., Takuma, N., Niino, H., and Sagesaka, Y. M. Effects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial. BMC.Complement Altern.Med. 2011;11:15. View abstract.

Rogers, P. J., Smith, J. E., Heatherley, S. V., and Pleydell-Pearce, C. W. Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together. Psychopharmacology (Berl) 2008;195(4):569-577. View abstract.

Sadzuka, Y., Sugiyama, T., Suzuki, T., and Sonobe, T. Enhancement of the activity of doxorubicin by inhibition of glutamate transporter. Toxicol.Lett 9-15-2001;123(2-3):159-167. View abstract.

Sugiyama, T. and Sadzuka, Y. Theanine and glutamate transporter inhibitors enhance the antitumor efficacy of chemotherapeutic agents. Biochim.Biophys.Acta 12-5-2003;1653(2):47-59. View abstract.

Sugiyama, T. and Sadzuka, Y. Theanine, a specific glutamate derivative in green tea, reduces the adverse reactions of doxorubicin by changing the glutathione level. Cancer Lett. 8-30-2004;212(2):177-184. View abstract.

Sugiyama, T., Sadzuka, Y., Nagasawa, K., Ohnishi, N., Yokoyama, T., and Sonobe, T. Membrane transport and antitumor activity of pirarubicin, and comparison with those of doxorubicin. Jpn J Cancer Res 1999;90(7):775-780. View abstract.

Terashima, T., Takido, J., and Yokogoshi, H. Time-dependent changes of amino acids in the serum, liver, brain and urine of rats administered with theanine. Biosci.Biotechnol.Biochem. 1999;63(4):615-618. View abstract.

Yang, Q. S., Xu, P. X., Li, Y. H., Jiang, S., Zhang, X., and Xue, M. [Effects of theanine and houpu extract in 7-day chick social separation-stress procedure]. Zhongguo Zhong.Yao Za Zhi. 2007;32(19):2040-2043. View abstract.

Yokogoshi, H., Kato, Y., Sagesaka, Y. M., Takihara-Matsuura, T., Kakuda, T., and Takeuchi, N. Reduction effect of theanine on blood pressure and brain 5-hydroxyindoles in spontaneously hypertensive rats. Biosci.Biotechnol.Biochem. 1995;59(4):615-618. View abstract.

Camfield DA, Stough C, Farrimond J, Scholey AB. Actue effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis. Nutr Rev. 2014;72(8):507-522. View abstract.

Dodd FL, Kennedy DO, Riby LM, Haskell-Ramsay CF. A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood. Psychopharmacology. 2015;232(14):2563-2576. View abstract.

Foxe JJ, et al. Assessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention task. Neuropharmacology. 2012;62(7):2320-2327. View abstract.

Graham HN. Green tea composition, consumption, and polyphenol chemistry. Prev Med 1992;21:334-50. View abstract.

Kakuda T, Nozawa A, Unno T, et al. Inhibiting effects of theanine on caffeine stimulation evaluated by EEG in the rat. Biosci Biotechnol Biochem 2000;64:287-93. View abstract.

Kakuda T, Yanase H, Utsunomiya K, et al. Protective effect of gamma-glutamylethylamide (theanine) on ischemic delayed neuronal death in gerbils. Neurosci Lett 2000;289:189-92. View abstract.

Kimura R, Murata T. Effect of theanine on norepinephrine and serotonin levels in rat brain. Chem Pharm Bull 1986;34:3053-57.

Lu K, Gray MA, Oliver C, et al. The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans. Hum Psychopharmacol 2004;19:457-65. View abstract.

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;16(4):348-354. View abstract.

Miyachi T, et al. Perioperative oral administration of cystine and theanine enhances recovery after distal gastrectomy: a prospective randomized trial. JPEN. 2013;37(3):384-391. View abstract.

Sadzuka Y, Sugiyama T, Miyagishima A, et al. The effects of theanine, as a novel biochemical modulator, on the antitumor activity of adriamycin. Cancer Lett 1996;105:203-9. View abstract.

Sadzuka Y, Sugiyama T, Sonobe T. Efficacies of tea components on doxorubicin induced antitumor activity and reversal of multidrug resistance. Toxicol Lett 2000;114:155-62. View abstract.

Sadzuka Y, Sugiyama T, Sonobe T. Improvement of idarubicin induced antitumor activity and bone marrow suppression by theanine, a component of tea. Cancer Lett 2000;158:119-24. View abstract.

Sakato Y. The chemical constituents of tea: III. A new amide theanine. Nippon Nogei Kagakukaishi 1949;23:262-267.

Scheid L, et al. Kinetics of L-theanine uptake and metabolism in healthy participants are comparable after ingestion of L-theanin via capsules and green tea. J Nutr. 2012;142(12):2091-2096. View abstract.

Sugiyama T, Sadzuda Y. Enhancing effects of green tea components on the antitumor activity of adriamycin against M5076 ovarian sarcoma. Cancer Lett 1998;133:19-26. View abstract.

Sugiyama T, Sadzuka Y, Tanaka K, Sonobe T. Inhibition of glutamate transporter by theanine enhances the therapeutic efficacy of doxorubicin. Toxicol Lett 2000:121:89-96. View abstract.

Sugiyama T, Sadzuka Y. Combination of theanine with doxorobucin inhibits hepatic metastasis of M5076 ovarian sarcoma. Clin Cancer Res 1999;5:413-6. View abstract.

Unno K, et al. Anti-stress effect of theanine on students during pharmacy practice: positive correlation among salivary a-amylase activity, trait anxiety and subjective stress. Pharmacol Biochem Behav. 2013;111:128-135. View abstract.

Williams J, Kellett J, Roach PD, et al. L-theanine as a functional food additive: its role in disease prevention and health promotion. Beverages 2016;2(2):13.

Yokogoshi H, Kobayashi M. Hypotensive effect of gamma-glutamylethylamide in spontaneously hypertensive rats. Life Sci 1998;62:1065-8. View abstract.

Yokogoshi H, Mochizuki M, Saitoh K. Theanine-induced reduction of brain serotonin concentration in rats. Biosci Biotechnol Biochem 1998;62:816-7. View abstract.

Yokozawa T, Dong E. Influence of green tea and its three major components upon low-density lipoprotein oxidation. Exp Toxicol Pathol 1997;49:329-35. View abstract.

Yokozawa T, Oura H, Nakagawa H, et al. Effects of a component of green tea on the proliferation of vascular smooth muscle cells. Biosci Biotechnol Biochem 1995;59:2134-6. View abstract.

Yoto A, Motoki M, Murao S, Yokogoshi H. Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses. J Physiol Anthropol. 2012;31:28. View abstract.

Zheng G, Sayama K, Okubo T, et al. Anti-obesity effects of three major components of green tea, catechins, caffeine and theanine, in mice. In Vivo 2004;18:55-62. View abstract.

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