A reference work, not a recommendation to use: this profile describes mechanism and evidence and does not replace medical advice. The claims come from marketing and forums and are tested here, not endorsed.

Mechanism of action

Evidence map: L-Theanine

Each line stands for a published finding; line style and color show where it comes from. The filter hides weaker evidence levels. Sources: see references.

In rats, after administration into the stomach, L-theanine reaches the brain via a leucine-preferring transport system; serotonin and dopamine rose mainly in the striatum, hypothalamus, and hippocampus, and when given directly into the striatum, theanine released dopamine, which an NMDA antagonist markedly attenuated [1]. At glutamate receptors from rat neurons, theanine binds only very weakly: its IC50 was 80- to 30,000-fold above that of glutamate [2]. A later study from the same group found no effect on receptor binding, but did find inhibition of glutamine uptake in neurons and astrocytes and, at very high concentration, reduced glutamate release [3].

In humans, L-theanine from capsules and from green tea is absorbed equally well; peak plasma levels are reached after about 0.8 hours, and it is apparently cleaved to ethylamine and glutamic acid [4]. Possible effects may therefore come from theanine itself or from these cleavage products [4]. A review summarizes that reports of increased alpha waves on EEG, less stress, and better sleep are often inconsistent, that many studies come from one region and from one manufacturer, and that animal experiments show a good safety profile [5].

Assigned to the site of action NMDA receptor (GluN1/GluN2B) in the postsynaptic membrane of a dendritic spine; not drawn in its figure: only very weak binding to glutamate receptors.

Targets

TargetTypeActionKey dataEvidence
Ionotropic glutamate receptors (AMPA, kainate, NMDA glycine site)ReceptorBindingIC50 80- to 30,000-fold higher than glutamate (rat neurons) Laboratory[2]
Glutamine transporterTransporterInhibitorinhibition of glutamine uptake at 0.1–10 mM (rat cells) Laboratory[3]

Effect profile

Which signaling systems the compound affects according to current data. ↑ enhanced, ↓ dampened, ≈ modulated, ○ no effect; dots = evidence level.

  • Dopamine↑ · More dopamine in the striatum and dopamine release after injection (rat)[1]
  • Noradrenalineno data
  • Serotonin↑ · More serotonin in the striatum, hypothalamus, and hippocampus (rat)[1]
  • Acetylcholineno data
  • Glutamate · AMPAunclear · Very weak binding in one study, no effect on binding in a later one[2][3]
  • Glutamate · NMDAunclear · Inhibits glutamine uptake and, at high concentration, reduces glutamate release (cell culture)[2][3]
  • GABAno data
  • Histamineno data
  • Orexinno data
  • Adenosineno data
  • Opioidsno data
  • Melatoninno data
  • Neurotrophinsno data
  • Blood flowno data
  • Nitric oxideno data
  • Energy metabolismno data
  • Insulin · glucoseno data
  • Inflammation · oxidativeno data
  • Stress axisno data
  • Testosterone axisno data
  • Endocannabinoidsno data
  • Autophagy · senescenceno data
  • Immune systemno data
  • Lipid metabolismno data
  • Coagulation · fibrinolysisno data
  • Methylationno data

Human studies

  • Absorption and breakdown

    randomized, crossover · healthy · n = 12 · Single doses

    Measured: Plasma, erythrocyte, and urine levels

    Result: Capsule and tea equivalent; peak level after 0.8 hours; cleavage to ethylamine and glutamic acid.[4]

    Human, randomised

  • Meta-analysis of tea, theanine, and theanine plus caffeine

    systematic review and meta-analysis of RCTs (50 RCTs, 15 in meta-analyses) · healthy · mostly acute (1st–2nd hour)

    Measured: Cognition, mood, sleep

    Result: Theanine alone: faster choice reaction time (SMD −0.35); with caffeine, small to medium advantages over placebo, often with wide confidence intervals. Partly funded by a tea manufacturer.[6]

    Human, randomised

  • Meta-analysis of theanine and cognition

    meta-analysis of placebo-controlled RCTs (5 studies) · healthy · n = 148 · acute to a few weeks

    Measured: Reaction times, Stroop test

    Result: Faster recognition reaction time (MD −15.2 ms); simple reaction time and Stroop test without a significant effect.[7]

    Human, randomised

  • Stress, sleep, and cognition over four weeks

    RCT, double-blind, placebo-controlled, crossover · healthy · n = 30 · 4 weeks per phase

    Measured: Questionnaires on stress and sleep, cognitive tests

    Result: Better scores on stress and sleep questionnaires as well as on verbal fluency and executive function; product supplied by the manufacturer, two authors employed there.[8]

    Human, randomised

Risks and warnings

  • Few long-term data

    No toxicity in animal experiments up to the highest amount tested; controlled long-term studies in humans are lacking, and the authors of a review advise caution at pharmacological amounts [5].

    Animal study

Fact check: common claims

  • partly supported

    “L-Theanine improves concentration and attention”

    Faster reaction times in individual tests, other tests without an effect; few, small studies [6][7].

  • not supported

    “L-Theanine enhances the focus effect of caffeine and mitigates its side effects”

    The combination works better than placebo [6], but a separate contribution of theanine over caffeine alone has not been shown; EFSA explained the attention effect of black tea by its caffeine [9].

  • partly supported

    “L-Theanine increases alpha waves and has a relaxing effect”

    Individual studies report more alpha activity and less stress, but the findings are often inconsistent [5].

  • partly supported

    “L-Theanine improves sleep”

    In a small, manufacturer-related RCT, self-reported sleep quality improved [8]; according to a review, high-quality studies on falling asleep and staying asleep are lacking [5].

Pharmacokinetics

Absorption
Rapid; peak plasma levels after about 0.8 hours, comparable from capsules and tea [4].
Half-life
Not reported as a numerical value; measurements up to 24 hours [4].
Metabolism
Presumably cleaved to ethylamine and glutamic acid; also excreted unchanged in urine [4].
Entry into the brain
In rats, into the brain via a leucine-preferring transport system [1].

Legal status

Germany
Constituent of tea and dietary supplements; status under food law not verified.
EU
A health claim for L-theanine was rejected, according to a review, on the basis of an EFSA assessment [5]. EFSA attributed the attention-enhancing effect of black tea to its caffeine [9].
USA
Not verified.

Open questions

  • Does L-theanine itself act, or do its cleavage products ethylamine and glutamic acid?
  • Does L-theanine in combination with caffeine contribute anything that caffeine alone does not?
  • Do independent, larger RCTs confirm the effects on reaction time, stress, and sleep?

References

  1. Yokogoshi H, Kobayashi M, Mochizuki M, Terashima T. Effect of theanine, r-glutamylethylamide, on brain monoamines and striatal dopamine release in conscious rats. Neurochem Res. 1998;23(5):667–73. doi:10.1023/a:1022490806093 · PubMed
  2. Kakuda T, Nozawa A, Sugimoto A, 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):2683–6. doi:10.1271/bbb.66.2683 · PubMed
  3. Kakuda T, Hinoi E, Abe A, Nozawa A, Ogura M, Yoneda Y. Theanine, an ingredient of green tea, inhibits [3H]glutamine transport in neurons and astroglia in rat brain. J Neurosci Res. 2008;86(8):1846–56. doi:10.1002/jnr.21637 · PubMed
  4. Scheid L, Ellinger S, Alteheld B, Herholz H, Ellinger J, Henn T, et al. Kinetics of L-theanine uptake and metabolism in healthy participants are comparable after ingestion of L-theanine via capsules and green tea. J Nutr. 2012;142(12):2091–6. doi:10.3945/jn.112.166371 · PubMed
  5. Dashwood R, Visioli F. L-theanine: from tea leaf to trending supplement – does the science match the hype for brain health and relaxation? Nutr Res. 2025;134:39–48. doi:10.1016/j.nutres.2024.12.008 · PubMed
  6. Payne ER, Aceves-Martins M, Dubost J, Greyling A, de Roos B. Effects of tea (Camellia sinensis) or its bioactive compounds L-theanine or L-theanine plus caffeine on cognition, sleep, and mood in healthy participants: a systematic review and meta-analysis of randomized controlled trials. Nutr Rev. 2025;83(10):1873–91. doi:10.1093/nutrit/nuaf054 · PubMed
  7. Mátyus RO, Szikora Z, Bodó D, Vargáné Szabó B, Csupor É, Csupor D, et al. 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. J Clin Med. 2025;14(21):7710. doi:10.3390/jcm14217710 · PubMed
  8. Hidese S, Ogawa S, Ota M, Ishida I, Yasukawa Z, Ozeki M, et al. Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial. Nutrients. 2019;11(10):2362. doi:10.3390/nu11102362 · PubMed
  9. EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA); Turck D, Bresson JL, Burlingame B, Dean T, Fairweather-Tait S, et al. Black tea and improvement of attention: evaluation of a health claim pursuant to Article 13(5) of Regulation (EC) No 1924/2006. EFSA J. 2018;16(5):e05266. doi:10.2903/j.efsa.2018.5266 · PubMed
How this profile was checked

Last reviewed: 2026-10-23. All sources with a DOI or PMID were resolved automatically via Crossref or doi.org and PubMed.

Translated from the German profile (version of 2026-10-23); translation checked on 2026-10-26.

Checked

  • All 9 DOIs resolved via Crossref and all PMIDs via PubMed with tools/pruefe_profile.py.
  • Abstracts: transport into the brain, 5-HT/DA ↑, NMDA-dependent DA release [1]; IC50 80- to 30,000-fold [2]; no receptor effect, glutamine transport 0.1–10 mM, glutamate ↓ at 10 mM [3]; n = 12, Tmax 0.8 h, ethylamine and glutamic acid [4]; 50 RCTs, 15 meta-analyzed, SMD −0.35, funding by Lipton [6]; 5 RCTs, 148 people, MD −15.2 ms [7]; n = 30, crossover, conflict of interest [8]; black tea effect due to caffeine [9].
  • In the full text [5]: inconsistent findings on alpha waves, stress, sleep; many studies from one region and from one manufacturer; animal experiments without toxicity; rejection of a health claim for theanine on the basis of an EFSA assessment.
  • ClinicalTrials.gov: 57 entries for theanine (October 23, 2026).

Not verified

  • The 2011 EFSA opinion on L-theanine (DOI 10.2903/j.efsa.2011.2238) was not retrievable; content documented only via [5].
  • Status of L-theanine as an ingredient in the EU under food law not checked.
  • Whether the papers [2] and [3] come from a tea manufacturer (first author with a company address) was not examined further.

No dosages, no sources of supply. This information does not replace medical advice.

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