Theanine
Theanine is a non-proteinogenic amino acid structurally similar to glutamate and glutamine.12 Discovered as a constituent of green tea in 1949 and isolated from gyokuro leaves in 1950,34 it constitutes approximately 1-2% of dried green tea leaves.56 Used as a nootropic for its calming properties without significant sedation,2 theanine is frequently combined with caffeine to mitigate stimulant-related anxiety while potentially enhancing attention.72 It is widely available as a dietary supplement.8
Contents
Dosage & Duration
Dosage
Mildly stimulating at light to common doses, becoming sedating at strong doses around 300 mg. Headaches have been reported at doses well above 200 mg.
Duration
Subjective Effects
Theanine produces a subtle, low-intensity state most often described as relaxing without being sedating. Taken alongside caffeine it smooths and mellows the stimulant's character, taking the edge off jitteriness while leaving wakefulness intact. Taken on its own during a period of stress it can remove anxiety and establish a relaxed disposition lasting for some hours. The overall arc is gentle, with effects fading softly rather than producing a distinct comedown.
Physical
Physical effects are minimal and sit at the shallow end of noticeable, amounting to relaxation without the fuzziness or heaviness of sedation, though some tiredness or a worn feeling may persist.
Cognitive
The headspace is calm and settled, with a subtle perception of increased mental clarity; calmness and alertness coexist rather than trading off against one another.
Reagent Testing
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Pharmacology
Pharmacodynamics
Theanine is structurally similar to the excitatory neurotransmitter glutamate and binds to glutamate receptors, though with much lower affinity in comparison.9 It acts as an antagonist at AMPA and kainate receptors while functioning as a partial co-agonist at NMDA receptors.1011 Theanine also binds to group I metabotropic glutamate receptors and inhibits both glutamine and glutamate transporters, blocking their reuptake.121314 Beyond its direct glutamatergic activity, theanine increases dopamine, GABA, and glycine levels in various brain regions.1516 Its effects on serotonin remain unclear, with separate studies showing both increases and decreases in brain serotonin levels using similar experimental protocols.1517
Pharmacokinetics
Theanine is absorbed in the small intestine after oral ingestion.18 It undergoes hydrolysis to L-glutamate and ethylamine in both the intestine and liver, potentially functioning as a donor for glutamate synthesis.18
Tolerance
Harm Potential
Addiction & Dependence
Psychological
Extremely LowTheanine is not habit-forming and is not known to produce psychological dependence or compulsive use patterns.
Physical
Extremely LowTheanine is non-addictive and does not produce physical dependence.
Toxicity
Mild stomach upset has been reported following very large doses, though it may be attributable to concurrent food intake rather than the substance itself.
Headaches are occasionally reported at high doses well above 200mg; theanine is not known to cause brain damage and shows no negative cognitive consequences at reasonable doses in a careful context.
History & Culture
Theanine was discovered as a constituent of green tea in 1949. The following year, in 1950, a laboratory in Kyoto successfully isolated the compound from gyokuro leaves, a type of Japanese green tea known for its high theanine content. Japan approved its unlimited use in all foods except infant…
Legality
By Country
References
Citations
- Mátyus RO, Szikora Z, Bodó D, Vargáné Szabó B, Csupor É, Csupor D, & Tóth B. (2025). Promising, but Not Completely Conclusive—The Effect of l-Theanine on Cognitive Performance Based on the Systematic Review and Meta-Analysis of Randomized Placebo-Controlled Clinical Trials. Journal of Clinical Medicine, 14(21), 7710. https://doi.org/10.3390/jcm142177101
- (2025). L-theanine: From tea leaf to trending supplement - does the science match the hype for brain health and relaxation?. Nutrition Research, 134, 39–48. https://doi.org/10.1016/j.nutres.2024.12.008123
- Baba Y, Inagaki S, Nakagawa S, Kaneko T, Kobayashi M, & Takihara T. (2021). Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study. Journal of Medicinal Food. https://doi.org/10.1089/jmf.2020.48031
- Unno K, & Nakamura Y. (2021). Green Tea Suppresses Brain Aging. Molecules, 26(16), 4897. https://doi.org/10.3390/molecules261648971
- Kim S, Jo K, Hong KB, Han SH, & Suh HJ. (2019). GABA and l-theanine mixture decreases sleep latency and improves NREM sleep. Pharmaceutical Biology. https://doi.org/10.1080/13880209.2018.15576981
- Saeed M, Khan MS, Kamboh AA, Alagawany M, Khafaga AF, Noreldin AE, Qumar M, Safdar M, Hussain M, Abd El-Hack ME, & Chao S. (2020). L-theanine: an astounding sui generis amino acid in poultry nutrition. Poultry Science. https://doi.org/10.1016/j.psj.2020.07.0161
- (2008). The combined effects of L-theanine and caffeine on cognitive performance and mood. https://doi.org/10.1179/147683008x3015131
- (2024). The effects of L-theanine supplementation on the outcomes of patients with mental disorders: a systematic review. Nutritional Neuroscience. https://pmc.ncbi.nlm.nih.gov/articles/PMC11616108/1
- (2002). Inhibition by theanine of binding of [3H]AMPA, [3H]kainate, and [3H]MDL 105,519 to glutamate receptors. https://doi.org/10.1271/bbb.66.26831
- (August 2017). Characterization of l-Theanine Excitatory Actions on Hippocampal Neurons: Toward the Generation of Novel N-Methyl-d-aspartate Receptor Modulators Based on Its Backbone. ACS Chemical Neuroscience, 8(8), 1724–1734. https://doi.org/10.1021/acschemneuro.7b000361
- (August 2011). Neuroprotective effects of theanine and its preventive effects on cognitive dysfunction. Pharmacological Research, 64(2), 162–168. https://doi.org/10.1016/j.phrs.2011.03.0101
- (July 2004). Possible involvement of group I mGluRs in neuroprotective effect of theanine. Biochemical and Biophysical Research Communications, 320(1), 116–122. https://doi.org/10.1016/j.bbrc.2004.05.1431
- Oka N. (2008). Theanine, an ingredient of green tea, inhibits [3H]glutamine transport in neurons and astroglia in rat brain. Journal of Neuroscience Research. https://pubmed.ncbi.nlm.nih.gov/18293419/1
- (April 2001). Inhibition of glutamate transporter by theanine enhances the therapeutic efficacy of doxorubicin. Toxicology Letters, 121(2), 89–96. https://doi.org/10.1016/s0378-4274(01)00317-41
- (2006). The neuropharmacology of L-theanine(N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent. Journal of Herbal Pharmacotherapy, 6(2), 21–30. https://doi.org/10.1300/j157v06n02_0212
- Yamada T. (2005). Effects of theanine, r-glutamylethylamide, on neurotransmitter release and its relationship with glutamic acid neurotransmission. https://pubmed.ncbi.nlm.nih.gov/16493792/1
- (1998). Theanine-induced reduction of brain serotonin concentration in rats. https://doi.org/10.1271/bbb.62.8161
- (November 2013). Cystine and theanine: amino acids as oral immunomodulative nutrients. SpringerPlus, 2. https://doi.org/10.1186/2193-1801-2-63512
- Hagihara R, Ohno S, Hayashi M, Tabata K, & Endo H. (2021). Production of l-Theanine by Escherichia coli in the Absence of Supplemental Ethylamine. Applied and Environmental Microbiology, 87(11), e00031-21. https://doi.org/10.1128/aem.00031-211
- (2007-02-05). GRAS Notice Inventory: GRN No. 209, L-theanine. US Food and Drug Administration. https://hfpappexternal.fda.gov/scripts/fdcc/index.cfm?set=GRASNotices&id=2091
- (2019-06-03). L-THEANINE — Natural Health Products Ingredients Database (NHPID). Health Canada, Natural and Non-Prescription Health Products Directorate. https://webprod.hc-sc.gc.ca/nhpid-bdipsn/atReq?atid=l.theanine&lang=eng1
Automated synthesisInformation aggregated and synthesized using an autonomous workflow built by Josie Kins.
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