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Theanine

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.

Kamal Patel
Research analysis led by .
Reviewed by
Examine.com Team
Last Updated:

Summary of Theanine

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

What is theanine?

L-Theanine is an amino acid that is not common in the diet and not one of the essential amino acids or even one of the common nonessential amino acids. It is found in meaningful amounts in tea, but otherwise supplementation is the main source of it. L-Theanine has structural similarity to glutamine and both neurotransmitters that are produced from it (GABA and glutamate). It is known to reach the brain and influence its function following oral ingestion.

What are theanine's benefits?

A reduction in anxiety, stress, and greater ability to relax is its most likely effect, and while still somewhat preliminary, studies suggest a benefit for these purposes. This effect likely also leads to an increase in sleep quality due to deeper sleep, but it's not apparent whether or not it's effective for improving insomnia in general.

Other than that, the benefits are more murky, and while potential improvements in attention and executive function have been noted, but much more research is needed before having much confidence in that, and other cognitive benefits are dubious.

It may have a mild antagonistic effect on caffeine and reduce the high blood pressure and jitters, taking "the edge off", but more research is needed to confirm this.

Interestingly, the relaxing and attention promoting properties of L-theanine coupled with the lack of sedation may have its most significant supplemental role in attenuating the 'edge' of many stimulants. A combination of L-Theanine with caffeine (200mg each) is noted to be synergistic in promoting cognition and attention.

What are theanine's side-effects and drawbacks?

Very scarce research has suggested a potential reduction in alertness, which makes sense due to its calming effects. However, this research needs to be replicated and explored more deeply in more activity contexts.

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How to Take

Medical Disclaimer

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

Unlocked for Examine members

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.

Full details are available to Examine members.
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
Relaxation
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
Anxiety
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
Attention
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
Blood Pressure
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
Sleep Quality
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
Symptoms of Schizophrenia
Minor - See study
Activation and anxiety symptoms of schizophrenia appear to be reduced with high dose (400mg) Theanine
grade-c
Heart Rate
- 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
Reaction Time
- - 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
Sedation
- - See study
No apparent effect in one study.
grade-c
Subjective Well-Being
- - See study
No significant influence on subjective well being and mood state per se
grade-d
Stress
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
DHEAS
Minor - See study
One study found an increase when taken chronically.
grade-d
Executive Function
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
HDL-C
Minor - See study
One study found a decrease. Needs replication.
grade-d
Headaches

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
Insomnia
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
Interleukin 2

Minor 		- See study
An increase after exercise but not during recovery in one study.
grade-d
Prepulse Inhibition
Minor - See study
An increase from 200 and 400 but not 600 mg in one study.
grade-d
Serum BDNF
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
Treg Cells

Minor 		- See study
One study found an increase during a recovery phase, but not directly after exercise.
grade-d
Triglycerides
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
Aerobic Exercise
- - See study
No apparent effects on rowing time trials in one study.
grade-d
Alertness
- 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
Blood Lactate
- - See study
No apparent effect in one study.
grade-d
Cortisol
- Moderate See 2 studies
No apparent effect from acute or chronic supplementation.
grade-d
Creatinine
- - See study
No apparent effect in one study.
grade-d
DHEA
- - See study
No apparent effect in one study.
grade-d
Depression
- 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
Fatigue
- - See study
No apparent effect in one study.
grade-d
Granulocyte Count
- - See study
No apparent effect in one study.
grade-d
HbA1c
- - See study
No apparent effect in one study.
grade-d
Insulin
- - See study
No apparent effect in one study.
grade-d
Interferon Gamma
- - See study
No apparent effect in one study.
grade-d
Interleukin 10
- - See study
grade-d
Interleukin 4
- - See study
No apparent effect in response to exercise in one study.
grade-d
LDL-C
- - See study
No apparent effect in one study.
grade-d
Liver Enzymes
- - See study
No apparent effect in one study.
grade-d
Lymphocyte Count
- - See study
No apparent effect in one study.
grade-d
Mood
- High See all 3 studies
Inconsistent results during acute dosing and cognitive testing.
grade-d
Motor Speed
- Very High See 2 studies
No apparent effect in two studies.
grade-d
Natural Killer Cell Content
- - See study
No apparent effect in one study.
grade-d
Numerical Memory
- - See study
No apparent effect in one study.
grade-d
Power Output
- - See study
No apparent effect in rowing power output in one study.
grade-d
Processing Accuracy
- Very High See all 3 studies
No apparent effect in various cognitive tasks.
grade-d
Processing Speed
- - See study
No apparent effect in one study.
grade-d
Salivary Alpha-Amylase
- - See study
No apparent effect in one study.
grade-d
Total Antioxidant Capacity
- - See study
No apparent effect in one study over the course of 6 weeks.
grade-d
Total Cholesterol
- Very High See 2 studies
No apparent effect in two studies.
grade-d
Urea
- - See study
No apparent effect in one study.
grade-d
Verbal Fluency
- Moderate See 2 studies
Mixed evidence. Effect didn't seem to be particularly large in the positive study. More research is needed.
grade-d
Verbal Memory
- Moderate See 2 studies
Mixed evidence, not particularly notable in the positive study. More research is needed.
grade-d
Vigor/Activity
- - See study
No apparent effect in one study.
grade-d
White Blood Cell Count
- - See study
No apparent effect in one study.
grade-d
Working Memory
- Very High See all 3 studies
No apparent effect in 3 studies.

Studies Excluded from Consideration

Confounded with other nutrients.[1][2][3][4][5][6][7][8][9][10][11][12][13][6][14][15][16][17]

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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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Research Breakdown on Theanine

1Sources and Composition

1.1Sources

1.2Structure and Properties

1.3Types of Theanine

2Pharmacology

2.1Metabolism

2.2Interactions

3Longevity

3.1C. Elegans

4Neurology

4.1Kinetics and Mechanisms

4.2Catecholamines

4.3Serotonin

4.4GABAergic mechanisms

4.5Glutaminergic mechanisms

4.6Sedation

4.7Schizophrenia

4.8Neuroimmunology

4.9Memory

4.10Seizures

4.11Anxiety

4.12Attention and ADHD

4.13Stress

5Cardiovascular Health

5.1Blood Flow

6Nutrient-Nutrient Interactions

6.1Caffeine

6.2Green Tea

6.3Glutamine

7Safety and Toxicology

7.1General
Click here to see all 94 references.

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This page is regularly updated, to include the most recently available clinical trial evidence.

Each member of our research team is required to have no conflicts of interest, including with supplement manufacturers, food companies, and industry funders. The team includes nutrition researchers, registered dietitians, physicians, and pharmacists. We have a strict editorial process.

This page features 94 references. All factual claims are followed by specifically-applicable references. Click here to see the full set of research information and references for Theanine.

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