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Theanine

L-theanine is a naturally occurring, non-protein amino acid found in tea that promotes relaxation by reducing stress and anxiety levels. Although L-theanine is not a sedative and does not cause drowsiness, it may help improve sleep quality by promoting a more relaxed state. L-theanine supplementation has also been shown to have positive effects on aspects of cognitive function, especially when taken with caffeine.

Our evidence-based analysis on theanine features 95 unique references to scientific papers.

Research analysis led by and reviewed by the Examine team.
Last Updated:

Summary of Theanine

Primary information, health benefits, side effects, usage, and other important details

What is L-theanine?

L-theanine is a naturally occurring non-proteinogenic amino acid that is found in tea and other natural sources. Unlike the 20 standard proteinogenic amino acids that are encoded in the genetic code and incorporated into proteins in the body, non-proteinogenic amino acids such as L-theanine are not used as building blocks for protein synthesis. Depending on the type of tea, L-theanine content is generally present in amounts under 50 mg per serving. When higher doses are desired, L-theanine is also commonly taken as a dietary supplement.

What are L-theanine’s main benefits?

The main benefits of L-theanine are associated with promoting a relaxed state without causing drowsiness. L-theanine may also have mild cognitive-enhancing effects, especially when taken with caffeine.[1] L-theanine has also been shown to suppress the blood pressure increasing effects of caffeine[2] and may also counteract blood pressure increases under stressful conditions.[3] Though it does not provide any sedative-like effects, L-theanine enhances sleep quality by promoting a more relaxed state in the brain.[4] 

What are L-theanine’s main drawbacks?

L-theanine has remarkably low toxicity, with one rodent study failing to find any toxic effects at 4,000 mg of L-theanine per kg of body weight daily for 13 weeks.[5] Additional animal studies have reported similar results with no observed toxicity at remarkably high doses, and L-theanine seems to be equally well-tolerated in humans, with no known reports of adverse effects or toxicity. Due to the ability of L-theanine to reduce blood pressure in certain contexts, people taking prescription blood pressure medication should consult with their physician before taking L-theanine supplements.

How does L-theanine work?

After consumption, L-theanine can cross the blood-brain barrier[6] and affect brain activity by promoting increased alpha-waves,[7] a pattern of brain activity associated with a more relaxed state. The tendency of L-theanine to increase alpha waves may explain its stress and anxiety reducing effects.[8] In animal studies, L-theanine has been shown to affect neurotransmitter signaling in the brain, but these effects have been less explored in humans. The mechanisms behind the synergistic effect of L-theanine and caffeine on cognition are not completely understood, but its relaxation-promoting properties are likely responsible for the reduced anxiousness and jitters associated with caffeine use.

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How to Take

Recommended dosage, active amounts, other details

L-Theanine tends to be taken in the dosage of 100-200mg, usually alongside caffeine

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Human Effect Matrix

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The Human Effect Matrix summarizes human studies to tell you what effects Theanine has on your body, how much evidence there is, and how strong these effects are.

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Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
Notes
grade-b Notable Very High See all 4 studies
A notable increase in relaxation (usually without sedation) appears to occur, as assessed by neural measurements (such as alpha-waves) or self-report surveys. Occurs within 30 minutes to an hour
grade-b Minor Low See all 8 studies
A potential reduction has been noted in various studies, though it is generally small and not particularly consistent, especially in the one study where participants all had generalized anxiety disorder. It may have the ability to reduce anxiety due to a challenging task acutely.
grade-c Minor Very High See all 7 studies
The ability to improve performance on some mental tasks that require a high degree of attention has been noted with acute dosing, but it doesn't seem to be particularly consistent. Little evidence exists for long-term effects, and the main study that evaluated them could have been observing the effects of improved sleep quality rather than anything inherent to theanine.
grade-c Minor Low See all 4 studies
As far as we can tell, it can reduce blood pressure increases in response to caffeine or acute stress, but it's unclear if it has any chronic effects.
grade-c Minor Very High See all 3 studies
Sleep quality has been noted to improve in persons with hyperactivity during sleep (such as ADHD), major depression, and healthy participants, but more research is needed. It's not clear if sleep time and sleep latency are affected.
grade-c Minor - See study
Activation and anxiety symptoms of schizophrenia appear to be reduced with high dose (400mg) Theanine
grade-c - Very High See all 4 studies
It can potentially reduce the increase in response to stress, but most studies have found no general effect.
grade-c - - See all 6 studies
Increases, decreases, and no effect have all been found in different studies. It's unclear if or when theanine has a consistent effect.
grade-c - - See study
No apparent effect in one study.
grade-c - Very High See all 4 studies
No significant influence on subjective well being and mood state per se
grade-d Notable Very High See 2 studies
More research is needed, but there's a notable reduction in response to acute stress in the available research.
grade-d Minor - See study
One study found an increase when taken chronically.
grade-d Minor High See all 3 studies
Potentially a small increase but the evidence is weak, and one study found a decrease. Much more research is needed.
grade-d
Minor
- See study
An increase was found with theanine alone when taken acutely, but theanine didn't reduce the headache-reducing effect of caffeine in one study. Much more research is needed.
grade-d Minor - See study
One study found a decrease. Needs replication.
grade-d Minor - See study
Insomnia severity was reduced modestly in one study in participants with generalized anxiety disorder who took it for 8 weeks.
grade-d
Minor
- See study
An increase after exercise but not during recovery in one study.
grade-d Minor - See study
An increase from 200 and 400 but not 600 mg in one study.
grade-d Minor - See study
One study found an increase from 8 weeks of 400 mg daily in schizophrenia patients. Much more research is needed.
grade-d
Minor
- See study
One study found an increase during a recovery phase, but not directly after exercise.
grade-d Minor - See study
One uncontrolled study found an increase over the course of 8 weeks. It's unclear if it was due to theanine or other changes.
grade-d - - See study
No apparent effects on rowing time trials in one study.
grade-d - High See all 3 studies
Either no effect or a decrease in one study, possibly due to its relaxing effects, but the experiment needs to be replicated.
grade-d - - See study
No apparent effect in one study.
grade-d - Moderate See 2 studies
No apparent effect from acute or chronic supplementation.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in one study.
grade-d - Low See all 3 studies
One uncontrolled trial found a reduction in major depression, while studies in participants with generalized anxiety and healthy participants didn't find effects. Much more research is needed to have confidence in its effects.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in one study.
grade-d - See study
In one 8-week study, theanine had no effect on IL-10 levels at rest or immediately after a bout of intense exercise, but did lower IL-10 levels the day after said exercise, though the decrease wasn't statistically significant compared to a placebo.
grade-d - - See study
No apparent effect in response to exercise in one study.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in one study.
grade-d - Very High See 2 studies
No apparent effect in two studies.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in rowing power output in one study.
grade-d - Very High See all 3 studies
No apparent effect in various cognitive tasks.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in one study over the course of 6 weeks.
grade-d - Very High See 2 studies
No apparent effect in two studies.
grade-d - - See study
No apparent effect in one study.
grade-d - Moderate See 2 studies
Mixed evidence. Effect didn't seem to be particularly large in the positive study. More research is needed.
grade-d - Moderate See 2 studies
Mixed evidence, not particularly notable in the positive study. More research is needed.
grade-d - - See study
No apparent effect in one study.
grade-d - - See study
No apparent effect in one study.
grade-d - Very High See all 3 studies
No apparent effect in 3 studies.

Studies Excluded from Consideration

Confounded with other nutrients.[9][10][11][12][13][14][15][16][17][18][19][20][21][14][22][23][24][25]

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Things to Note

Is a Form Of

Primary Function:

Also Known As

L-Theanine, 5-N-Ethyl-Glutamine, γ-glutamylethylamide

Goes Well With

  • Theanine is relaxing, but does not appear to induce sedation (cause sleep)

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Click here to see all 95 references.