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 L-Theanine | |
| Clinical data | |
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| Other names | γ-L-Glutamylethylamide |
| Dependence liability | None |
| Routes of administration | Oral |
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| Legal status | |
| Legal status | |
| Pharmacokinetic data | |
| Onset of action | ~1 hour[1] |
| Eliminationhalf-life | Capsule: ~1.2 hours Green Tea: ~0.8 hours[1] |
| Identifiers | |
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| CAS Number | |
| PubChemCID | |
| DrugBank | |
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| UNII | |
| KEGG | |
| ChEBI | |
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| CompTox Dashboard(EPA) | |
| ECHA InfoCard | 100.019.436 |
| Chemical and physical data | |
| Formula | C7H14N2O3 |
| Molar mass | 174.200 g·mol−1 |
| 3D model (JSmol) | |
| Melting point | 174.20 °C (345.56 °F)[3] |
| Boiling point | 215 °C (419 °F)[3] |
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Theanine/ˈθiːəniːn/, also known asL-γ-glutamylethylamide,N5-ethyl-L-glutamine,or γ-glutamylethylamide, is a bioactive,non-proteinogenic amino acid similar to theproteinogenic amino acidsglutamic acid andL-glutamine. It is produced by certain plants such as thetea plant (Camellia sinensis), and by somefungi.[3][4] Theanine was discovered in 1949 as a constituent ofgreen tea and was isolated in 1950 fromgyokuro tea leaves.[5] Theanine constitutes about 1–2% of the dry weight of green tea leaves.[4]
Theanine is sold as adietary supplement.[4] It is packaged ingelatin capsules,tablets, and as apowder, and may be an ingredient in branded supplements withcaffeine. It is also used as aningredient in food and beverages. Japan approved its unlimited use in all foods (including chocolates, soft drinks, and herb teas) except infant food in 1964,[4][6] and the USFood and Drug Administration has considered it to besafe at doses up to 250milligrams (mg) per serving since 2007.[7]
In 2011, theEuropean Food Safety Authority found there was insufficient evidence for acausal relationship between theanine consumption and improved cognitive function, alleviation of psychological stress, maintenance of normal sleep, or reduction of menstrual discomfort.[8] A 2025 review found that theanine has been poorly studied to date, having inconsistent research quality and unreliableclinical trials.[9]
The chemical nameN5-ethyl-L-glutamine[2] and other synonyms (see box) for theanine reflect its chemical structure. The name theanine, without prefix, is generally understood to imply theL- (S-)enantiomer, derived from the relatedproteinogenic L-amino acidglutamic acid. Theanine is an analog of this amino acid, and its primaryamide,L-glutamine (also a proteinogenic amino acid). Theanine is a derivative of glutamine that is ethylated on theamide nitrogen (as the nameN5-ethyl-L-glutamine describes), or alternatively, to the amide formed fromethylamine andL-glutamic acid at its γ- (5-) side chaincarboxylic acid group (as the name γ-L-glutamylethylamide describes).[citation needed]
Relative to theanine, the opposite (D-,R-) enantiomer is largely absent from the literature,[2] except implicitly. While natural extracts that are not harshly treated are presumed to contain only thebiosyntheticL- enantiomeric form, mishandled isolates and racemic chemical preparations of theanines necessarily contain both theanine and itsD-enantiomer (and fromracemic syntheses, in equal proportion), and studies have suggested that theD-isomer may actuallypredominate in some commercial supplement preparations.[10][11] Amino acidracemization in aqueous media is a well-established chemical process promoted by elevated temperature and non-neutral pH values; prolonged heating ofCamellia extracts—possible for oversteeped teas and in undisclosed commercial preparative processes—has been reported to result in increasing racemization of theanine to give increasing proportions of the nonnatural D-theanine, up to equal proportions of each enantiomer.[11]
Theanine is found primarily in plant and fungal species. It was discovered as a constituent of tea (Camellia sinensis) in 1949, and in 1950 a laboratory in Kyoto[12] successfully isolated it fromgyokuro leaf, which has high theanine content.[13] Theanine is substantially present in black, green, and whiteteas fromCamellia sinensis in quantities of about 1% of the dry weight.[14][15] Deliberately shading tea plants from direct sunlight, as is done formatcha andgyokuro green tea, increases L-theanine content.[16] TheL-enantiomer[2] is the form found in freshly prepared teas and some human dietary supplements.[11]
As astructural analog ofglutamate andglutamine, the theanine in teas or supplements is absorbed in thesmall intestine after oral ingestion; itshydrolysis toL-glutamate andethylamine occur both in the intestine and liver, possibly functioning as a donor for glutamate synthesis.[17]
Theanine is structurally similar to the excitatory neurotransmitterglutamate and binds toglutamate receptorsin vitro, though with much lower affinity in comparison. Specifically, it binds toionotropic glutamate receptors in themicromolar range, including theAMPA andkainate receptors and, to a lesser extent, theNMDA receptor.[18][19] It acts as anantagonist of the former two sites, and apartial co-agonist of theNMDA receptors.[20] In vitro, theanine also binds togroup ImGluRs.[18][21] In addition, it inhibitsglutamine transporters andglutamate transporters, and thus blocks thereuptake of glutamine and glutamate.[19][22]
Theanine may elicitumami taste, a consequence potentially associated with binding to and activation of theT1R1 +T1R3heterodimer orumami (savory) taste receptor.[23]
The regulatory status of theanine varies by country. It is sold as a dietary supplement across the United States and European Union.[4][24] In Japan,L-theanine has been approved for use in all foods, with some restrictions in the case of infant foods.[12][25] In the United States, the FDA considers it to beGRAS and allows its use as an ingredient in foods and beverages up to a maximum of 250 mg per serving.[7]
In 2003, the German Federal Institute for Risk Assessment (Bundesinstitut für Risikobewertung, BfR), an agency of theirFederal Ministry of Food and Agriculture, objected to the addition of isolated theanine to beverages.[26][27] While it was estimated the quantity of green tea consumed by the average Japanese tea drinker per day contains about 20 mg of the substance, there were no studies measuring the amount of theanine being extracted by typical preparation methods, or the percentage lost by discarding the first infusion. Therefore, with the Japanese being exposed to possibly much less than 20 mg per day, it was the opinion of the BfR thatpharmacological reactions to drinks typically containing 50 mg of theanine per 500 milliliters could not be excluded –reactions such as impairment ofpsychomotor skills and amplification of thesedating effects ofalcohol andhypnotics.[28]
On November 13, 2023, an Inspection by the Administration of Food Safety, Veterinary Medicine and Plant Protection of the Republic of Slovenia banned the sale ofPrime energy drinks in Slovenia as they containL-theanine, which is not allowed in non-alcoholic beverages. Prime Hydration may be freely sold.[29]
Theanine supplements have been marketed with a variety of claims that they improve cognitive performance, reduce stress, improve sleep quality, and alleviatemenstrual cramps. Evaluating these claims in 2011, the European Food Safety Authority assessed they were not supported by evidence in studies provided at that time.[8]
A 2020 review of low-quality studies suggested thatL-theanine supplementation of 200–400milligrams per day may reduce stress and anxiety in people with acute stress, but there was insufficient evidence for the use ofL-theanine as amedication to treat stress and anxiety.[30][better source needed] A 2024 review indicated thatL-theanine supplementation may be more effective than placebo in alleviating psychopathological symptoms associated withanxiety disorders,ADHD, andschizophrenia.[31]
A 2025 review reported that theanine research has lacked rigor, was mainly based onanecdotes, had ill-defined mechanisms, and exhibited unreliable clinical trials.[9]
