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L-Theanine is one of the main active ingredients found in green tea, alongside caffeine and green tea catechins. It helps promote relaxation and reduce without drowsiness, making it potentially synergistic with caffeine.

Our evidence-based analysis on theanine features 94 unique references to scientific papers.

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Research Breakdown on Theanine

1Sources and Composition


L-Theanine is an non-dietary amino acid (not required in the diet to support life) that is also a nonprotein amino acid, not being able to be used to make enzymes; it is known technically as r-glutamylethylamide[18] and is commonly known as a sedative amino acid.

L-Theanine can be found in:

  • The leaves of camellia sinensis (source of green tea catechins and the plant used to produce green, black, and white teas) at 0.9-3.1% of the dry weight of the leaves[19][20] and said to range from 25-60mg per 200mL serving of tea (2.5g of dried tea leaves)[21]

  • C. japonica and C. sasanqua[22]

  • The mushroom Xerocomus badius[23]

Theanine is most well known to be associated with green tea (the most popular form of camellia sinensis) due to that being its first known source and since L-theanine comprises up to 50% of total amino acids in tea.[19]

1.2Structure and Properties

Structurally, L-theanine is quite similar to the neurotransmitters glutamate and GABA; modifying one of the carboxylic ends of glutamic acid (further from the amine group) with another amine group followed by an ethyl group will produce L-theanine.[24] The addition of an amide group to glutamate already produces glutamine, so the structure of theanine can also be said to be an ethylated derivative of glutamine.

It has been noted that theanine may be able to alter the taste perception by reducing bitter nodes (chocolate, zinc, caffeine, grapefruit)[25] due to being a substrate of the umami perception on the tongue;[26] it is actually synergistic with the umami research drug inosine 5'-monophosphate[27] and it is reported to be the sole agent in green tea that promotes the sensation of umami.

Theanine may be able to slightly negate the taste of bitter stimuli, and appears to be the molecules that mediates the umami taste of green tea

The fermentation process of tea leaves appears to reduce the overall content of L-theanine somewhat (not absolutely) whereas the drying process (40-55°C for 7.1-8.5 hours) appears to increase the overall percentage of the tea that is theanine by weight; younger plants have higher theanine contents than older plants.[20] 

1.3Types of Theanine

Suntheanine® is a brand of theanine said to be over 99% L-Theanine isomer and is said to be produced from a mixture of glutamine with an ethylamine derivative.[28] It is patented by Taiyo Kagaku co. (company information[29] and patent link[30]) and appears to be used in a variety of studies that want standardization of L-theanine.[28][31][32][33][22][21][10]

Suntheanine is a patented brand of theanine that appears to be quality assurred for over 99% L-Theanine by weight



It has been noted that theanine is metabolized in the kidneys via the phosphate independent variant of the enzyme glutaminase, and is not affected by the phosphate dependent version;[34] a similar metabolism as glutamine.


Intake of theanine (2% of drinking water) to rats that was sufficient to raise plasma theanine to 7763.3+/-3875.4nmol/g was able to raise plasma glycine 17.2% without influencing taurine, serine, glutamate, or glutamine; the increase in glycine was observable for one week only.[18]


3.1C. Elegans

In C. Elegans exposed to L-theanine at concentrations of 100-10,000nM, it appears that supplementation can extend lifespan by an average value of 3.6% and maximal lifespan (assessed by the 80th percentile) by 4.4%.[35] There was no apparent dose-dependnece, with the 100nM concentration actually being the most effective tested.[35]

In C.Elegans there is a very mild increase in lifespan associated with L-Theanine


4.1Kinetics and Mechanisms

Theanine has been found to cross the blood brain barier, as systemic injections[36] and oral intake[37] can increase brain concentrations of the compound which appears to be mediated via the leucine-preferring transport system[38] (the neutral amino acid transport[39]).

Following oral intake L-theanine reaches the brain within an hour and is elevated up to 5 hours, which it then proceeds to get eliminated ultimately having no concentrations left at 24 hours post oral intake (4,000mg/kg).[37] The concentrations reaching the brain at this oral dose are around 2µM/g[37] and serum concentrations in this study peaked at above 12.5µM/mL within an hour, and were reduced to similar concentrations as the brain at 16 hours.[37]

Specific brain organs that have been shown to have increases in theanine concentration following oral intake include the hippocampus.[40]

Orally administered L-Theanine supplementation is able to cross the blood brain barier

L-Theanine supplementation in the standard dosages (50-250mg) has been repeatedly noted to increase α-waves in otherwise healthy persons. This may only occur in persons with somewhat higher baseline anxiety[41][42] or under periods of stress (positive[31] and negative[43] results), but has been noted to occur during closed eye rest[22] as well as during visuospatial tasks[33] around 30-45 minutes after ingestion.[22][21] It appears that only the α-1 wave (8-10Hz) is affected, with no influence on α-2 wave (11-13Hz).[21]

α-waves (8-12Hz) are known to be associated with a state of relaxation[44] which has been noted to occur alongside α-wave promotion with L-theanine.[45] Beyond relaxation, increased α-waves are associated with selective attention mechanisms[46][47] and arousal/mental alertness.[48] These altered wave functions are said the be evidence that theanine has 'relaxing and attention promoting' properties.

One study has reported increased theta wave function, but with a combination supplement of both theanine (60mg) and green tea extract (360mg) taken thrice daily over 16 weeks.[10]

Theanine supplementation appears to cause an increase in alpha-1 wave production within 30-45 minutes following oral ingestion of standard supplemental doses. This increase in alpha-1 production is highly associated with the most common benefits of Theanine supplementation (relaxation and attention)


Dopamine and noradrenaline do not appear to be significantly influenced with oral intake of theanine in rats (2% of drinking water, sufficient to increas plasma theanine to 7763.3+/-3875.4nmol/g) over 3 weeks.[18]

Direct injections of theanine into the striarum also cause dose-dependent increases in dopamine secretion for 40 minutes before returning to baseline.[38]

10µM/kg injections of theanine have been noted to reduce noradrenaline by 16% and 9% at 30 and 75 minutes, respectively; this was abolished with coadministration of caffeine.[49]


Oral intake of theanine which increases plasma theanine to 7763.3+/-3875.4nmol/g (2% of rat drinking water) has failed to significantly influence serotonin concentrations.[18]

10µM/kg injections have failed to significantly influence serotonin levels per se, but have been able to attenuate a caffeine-induced increase in serotonin.[49]

L-Theanine at an oral dose of 2,000-8,000mg/kg in rats (human estimated dose of 320-1280mg/kg) cause a dose dependent increase in brain tryptophan and reduction of serotonin, reaching 20.5% and 15.5% at the highest dose.[50]

Technically has anti-serotonergic mechanisms, but this occurs at a very high dose and likely isn't relevant for standard oral supplementation

4.4GABAergic mechanisms

Injections of theanine (30µM/kg only; 15µM/kg being ineffective and all doses higher than 30µM/kg being ineffective) have been found to increase cerebral concentrations of GABA by 19.8% following.[36] 

Conversely, 4% L-theanine in the drinking water of rats has been noted to reduce extracellular GABA in the frontal cortex.

4.5Glutaminergic mechanisms

L-Theanine has been found to have affinity for all three glutamate receptor subsets with IC50 and Ki values (respectively) of 24.6+/-0.9µM/19.2+/-0.7µM (AMPA), 41.5+/-7.6µM/29.3+/-5.4µM (Kainate), and 347+/-47µM/329+/-44µM (NMDA); these were 80-30,000 fold less potent than the endogenous ligand L-glutamate.[51]

Theanine has been found to accumulate in glutaminergic neurons (via two mechanisms with KM values of 42.3μM and 1.88mM) with at least one being the glutamine transporter, as the two amino acids compete for uptake (glutamine inhibits with an IC50 of 329.2+/-59.5μM while the opposite inhibition is weaker, at greater than 1,000μM).[52] It has been noted that incubation with 1-10mM theanine was able to also suppress extracellular glutamate concentrations.[52]

Theanine is an antagonist of the NMDA receptors (albeit with fairly weak efficacy) and can inhibit synaptic release of glutamate via blocking the transporter competitively. Theanine may also reduce glutamate levels, but this is also a fairly weak mechanism requiring a high concentration of theanine

As an increase in calcium release[51] and dopamine stimulation[38] with high concentrations of Theanine (800µM) seem to be blocked with the NMDA antagonist D-2-amino-5-phosphonopentanoate, it appears that theanine may signal through NMDA receptors at high concentrations.

Oddly, some mechanisms of theanine are blocked by NMDA antagonists. This suggests that higher concentrations of theanine may have their properties dependent on NMDA signalling


Some studies that measure α-wave production also note that participants self-report a more relaxed state.[22]

Theanine (5-10mM/kg injections) were able to increase hexobarbital induced sleep time by 11-21%, but not in a dose dependent manner.[36]

ADHD tends to be associated with symptoms related with hyperactivity, such as restless leg syndrome or disturbed sleep;[53][54] in persons with ADHD (8-12 year old boys) given 200mg L-theanine twice daily for 6 weeks, sleep quality appears to be improved by reducing sleep activity (10%) and increasing sleep efficiency.[28]

In studies assessing sleep latency (time taken to fall asleep) and sleep duration (time elapsed between going to bed and waking in the morning), these parameters appear unaffected.[28] Additionally, supplemental doses of theanine to promote relaxation do not appear to have sedative side-effects.[22]


In persons with diagnosed schizophrenia or schizoaffective disorder given 400mg L-theanine in addition to standard antipsychotics, 8 weeks of supplementation was able to significantly reduce positive and general psychopathology symptoms and anxiety.[55]


Oral consumption of 2-4mg/kg L-Theanine daily to mice for 5 weeks via the drinking water was able to attenuate the toxic effects on memory of Abeta(1-42) injection, and appeared to work via suppressing proinflammatory responses via ERK/p38 and NF-kB.[56]


One study using a supplement called LGNC-07 (360mg of green tea extract and 60mg theanine; thrice daily dosing for 16 weeks) in persons with mild cognitive impairment based on MMSE scores, supplementation was associated with improved delayed recognition and immediate recall scores with no effect on verbal and visuospatial memory (Rey-Kim test).[10]


Theanine has been noted to have anticonvulsive properties at 2.5-10mM/kg injections against caffeine, although it was not effective against other agents such as picrotoxin or strychnine.[36] Elsewhere, oral intake of 4% theanine in the water of rats was noted to be protective against pilocarpine but augmented seizures from pentylenetetrazol; the authors suggested usage in treating limbic seizures but not generalized seizures[57] and hypothesized that the mechanism was related to reducing GABA concentrations in the frontal cortex.[57] A potentiation of seizures induced by pentylenetetrazol, a GABAA antagonist,[58] have been noted elsewhere with both green and black tea containing theanine.[59]

May have anti-seizure properties, but due to also being implicated in augmenting seizures (depending on the research drug used) and no current human studies its usage for controlling seizures is limited


A comparative study between L-theanine (200mg and alprazolam control; 1mg) on anticipatory anxiety has noted that while theanine promoted relaxation, both theanine and alprazolam failed to significantly reduce anxiety symptoms in the model of anticipatory anxiety.[43] Some other studies that measure state anxiety fail to find a difference between theanine and placebo at this dose.[42]

In studies assessing relaxation[42][41] or attention/reaction time,[42] it appears that only persons with high baseline anxiety note benefits associated with relaxation whereas those who are not anxious fail to outperform placebo.

4.12Attention and ADHD

In persons with mild cognitive impairment, a combination supplement of green tea extract (360mg) and theanine (60mg) over 16 weeks was able to improve selective attention as assessed by a Stroop test.[10]

An improvement in attention has been noted in otherwise healthy persons with high baseline anxiety, with no apparent effect on those with lower anxiety scores at baseline.[42]


Rats fed 0.3% of their drinking water as L-theanine appear to have less circulating corticosterone at rest[60][40] and after stress testing[61][40] to approximately half of control, and in hippocampal CA1 cells theanine appears to cause a shift away from NMDA-dependent long term potentiation (LTP) towards NMDA-indepedent potentiation[60] while protecting from stress-induced memory impairment at this oral dose.[40][61]

It is known that increases in corticosterone[62][63] and stress itself[64] are able to suppress LTP and memory processing in the hippocampus and the reduction of corticosterone is thought to underlie the memory preserving effects of theanine.[40][61]

Oral intake of L-theanine in rats at feasible dosages is able to reduce circulating biomarkers of stress with or without an actual stressor being present, and can reduce the adverse effects of stress such as memory impairment

Supplementation of 200mg Theanine prior to an arithmatic stress test has been noted to reduce perceived stress following the task and to attenuate the risk in salivary IgA concentrations (biomarker of stress) by approximately half at the conclusion of the task.[31]

Reductions of percieved stress have been reported in human subjects given oral theanine at the standard dosages

5Cardiovascular Health

5.1Blood Flow

Both green and black tea are known to be associated with enhanced vascular responsiveness[65][66] and can stimulate nitric oxide production.[67]

Theanine appears to promote nitric oxide formation via phosphoryating the endothelial variant of the nitric oxide enzyme (eNOS) on Ser 1177 with concentration dependent effects between 0.01-1µM (10µM being as effective as 0.01µM).[68] This phosphorylation and subsequent endothelial relaxation is PI3K/ERK dependent (not dependent on Akt).[68]

Theanine appears to promote nitric oxide formation at relatively low concentrations, and is likely practically relevant following oral ingestion

6Nutrient-Nutrient Interactions


In comparison to 50mg caffeine in isolation, the addition of 100mg of L-Theanine to the caffeine was able to beneficially influence parameters of accuracy and attention when it came to cognitive testing in otherwise healthy adults[69] which has been replicated elsewhere with similar doses in improving sustained attention and ratings of fatigue.[8] A study using these two doses (in isolation or in combination) did not note any differences in reducing the number of errors in a sustained attention task when comparing combination therapy against either in isolation.[70]

The usage of caffeine in isolation (150mg) is able to improve perceptions of fatigue, rapid visual information processing (RVIP), and reaction time while adding 250mg L-Theanine to this preserved those benefits while improving alertness and improving reaction time further and reducing ratings of headache (which increased in caffeine control).[71] Reaction time (as well as the ability to switch between tasks) has been improved with combination therapy at lower doses (50mg caffeine and 100mg L-Theanine)[69] with this study also noting an improvement in attention via less interference with distracting stimuli.[69]

At least one study noted that the increase in attention (assessed via tasks requiring switching of attention with some distracting stimuli) occurred independently of the subject's perception of alertness.[16]

6.2Green Tea

At least one study has noted that Theanine may have reduced bioavailability when consumed vicariously through Green Tea, as assessed by Caco-2 cell studies.[72] Theanine is absorbed via passive diffusion and is generally well absorbed with concentrations above 4mM being effluxed back out of intestinal cells, but under this dose had two-fold absorption into intestinal cells (apical to basolateral) relative to secretion and incubation with green tea noted that while absorption rate was only hindered 35% the efflux rate was increased dramatically.[72] Although no causation was shown, it was thought that small mounts of D-Theanine in green tea (2.2-4.7% of total content[73]) may have competed with absorption due to their lower absorption rates;[74] the authors cast doubt on this possibility though.[72]


Glutamine appears to share the same intestinal transporter as L-Theanine (a sodium-coupled brush border transporter) except with much higher affinity.[75] The kinetics of both glutamine[76] and L-Theanine[72] across the intestinal membrane is via passive diffusion, suggesting similar absorption kinetics. A study noting less absorption of L-Theanine in the form of green tea relative to Theanine suggested that glutamine in green tea could be responsible for this effect, but did not demonstrate this beyond the hypothesis.[72]

Tannic acid (a major constituent of green tea) may inhibit the mitochondrial glutamate transporter,[77] Tannic acid has not been investigated on the intestinal glutamine transporter (different than mitochondrial glutamate).

7Safety and Toxicology


It has been reported that (via a publication from Taiyo co; producers of Suntheanine®) that oral ingestion of 99% L-theanine has failed to produce toxicity in rats at either 6,500mg/kg for 2 weeks or 2,000mg/kg over 28 days. 5% of the diet as L-theanine for 78 weeks has also failed to produce toxic effects.[29] A 13 week toxicity test in rats has established a No Observable Adverse Effect Limit (NOAEL) of 4,000mg/kg bodyweight, which was the highest dose tested.[78]

In animal research, L-theanine appears to be remarkably safe as very high doses have failed to cause toxicity

In an Ames test for carcinogenicity, theanine has reportedly failed to produce a response (suggesting noncarcinogenic).[79]

L-Theanine does not appear to be carcinogenic


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