The DOI matches its Crossref record; 68 of the 68 references it cites were found in a registry or an index.
The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review
Open accessAbstract
The green tea amino acid, L-theanine (L-THE) is associated with several health benefits, including improvements in mood, cognition and a reduction of stress and anxiety-like symptoms. This systematic review evaluated the effect of pure L-THE intake, in the form of orally administered nutritional supplements, on stress responses and anxiety levels in human randomised controlled trials. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist, 9 peer-reviewed journal articles were identified where L-THE as a supplement was compared to a control. Our findings suggest that supplementation of 200-400 mg/day of L-THE may assist in the reduction of stress and anxiety in people exposed to stressful conditions. Despite this finding, longer-term and larger cohort clinical studies, including those where L-THE is incorporated into the diet regularly, are needed to clinically justify the use of L-THE as a therapeutic agent to reduce stress and anxiety in people exposed to stressful conditions.
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The source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“In a systematic review published in 2019 by Williams et al., l-theanine in its pure form at a daily dose of 200–400 mg reduced stress and anxiety in people under acute stress [4].”
From 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 (2025) · cites this paper as [4]
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“l-theanine has several beneficial effects, including the improvement of mood and cognition and reductions in stress and anxiety-like symptoms [4].”
From 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 (2025) · cites this paper as [4]
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“Based on preclinical and clinical evidence, caffeine and l-theanine are the two main constituents contributing to this effect [4].”
From 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 (2025) · cites this paper as [4]
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“but there is insufficient evidence to recommend L-theanine as a treatment for any associated clinical symptoms (32, 39, 40, 44).”
From Effects of L-theanine on cognition, mood and sleep: evidence from human trials (2026) · cites this paper as [32]
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“However, there is currently insufficient evidence for L-theanine to be recommended as a standalone or adjunctive therapeutic intervention for chronic stress or any psychiatric conditions.”
From Effects of L-theanine on cognition, mood and sleep: evidence from human trials (2026) · cites this paper as [32]
Experimental — accuracy not yet measured
The source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“Importantly, reviews of trials have consistently reported that this dose range appears to be safe and well-tolerated by participants, even over daily dosing for an extended period (13, 32, 39, 44, 45).”
From Effects of L-theanine on cognition, mood and sleep: evidence from human trials (2026) · cites this paper as [32]
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“The IC 50 was reported 80 to 30 000-fold less than that of glutamate.”
From How does the tea L-theanine buffer stress and anxiety (2022) · cites this paper as [24]
Experimental — accuracy not yet measuredThe cited source says what the claim attributes to it.
In the citing paper
“The most comprehensive systematic review of participant-reported outcome measures and physiological stress response data included nine randomized placebo-controlled trials (n = 270) and concluded that supplementation with 200–400 mg/day of L-theanine may assist in the reduction of stress and anxiety in people exposed to stressful situations (32).”
From Effects of L-theanine on cognition, mood and sleep: evidence from human trials (2026) · cites this paper as [32]
The cited source says what the claim attributes to it.
In the citing paper
“Overall, trials have indicated that supplementation with 200–400 mg/day of L-theanine can help to reduce both perceived and physiological markers of stress and anxiety in largely healthy adult samples, particularly during periods of acute stress.”
From Effects of L-theanine on cognition, mood and sleep: evidence from human trials (2026) · cites this paper as [32]
The cited source says what the claim attributes to it.
In the citing paper
“Supplementation with L-theanine has generally been reported to be well-tolerated in clinical trials.”
From Effects of L-theanine on cognition, mood and sleep: evidence from human trials (2026) · cites this paper as [32]
The cited source says what the claim attributes to it.
In the citing paper
“These studies have also reported this dosing range of L-theanine to be safe and well-tolerated.”
From Effects of L-theanine on cognition, mood and sleep: evidence from human trials (2026) · cites this paper as [32]
The cited source says what the claim attributes to it.
In the citing paper
“Consistent with its use and availability as a dietary supplement, the current evidence suggests L-theanine supports individuals with associated health complaints (e.g. difficulties with sleep, or experiencing a stressful event)”
From Effects of L-theanine on cognition, mood and sleep: evidence from human trials (2026) · cites this paper as [32]
In the citing paper
“Another mechanism involved in the anti-stress action is that L-theanine competes for the receptors of glutamate, including NMDA, AMPA and KA [24].”
From How does the tea L-theanine buffer stress and anxiety (2022) · cites this paper as [24]
In the citing paper
“The consumption of L-THE is associated with a sensation of relaxation, and is proposed to elicit acute stress-reducing effects [3] as well as providing the characteristic ‘umami’ flavour [6].”
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Citations
Cites
Preferred Reporting Items for Systematic Reviews and Meta-Analyses: the PRISMA statement
Moher, D., Liberati, A., Tetzlaff, J., Altman, D. G., & for the PRISMA Group (2009) · BMJ · doi:10.1136/bmj.b2535 · Cited by 83,823
Preferred reporting items for systematic reviews and meta-analyses: the PRISMA Statement.
(2009) · PubMed Central · Cited by 44,859
Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA Statement
Moher, D., Liberati, A., Tetzlaff, J., & Altman, D. G. (2009) · Journal of Clinical Epidemiology · doi:10.1016/j.jclinepi.2009.06.005 · Cited by 19,575
(2008) · Cited by 3,790
Assessing Risk of Bias in Included Studies
Higgins, J. P., & Altman, D. G. (2008) · Cochrane Handbook for Systematic Reviews of Interventions · doi:10.1002/9780470712184.ch8 · Cited by 3,396
Spielberger, C. D. (2010) · The Corsini Encyclopedia of Psychology · doi:10.1002/9780470479216.corpsy0943 · Cited by 2,535
McNair, D. M. (1992) · Medical Entomology and Zoology · Cited by 2,527
McEwen, B. S. (2000) · Brain Research · doi:10.1016/s0006-8993(00)02950-4 · Cited by 1,827
Flavonoids in Food and Their Health Benefits
Yao, L., JIANG, Y. M., SHI, J., Tomás-Barberán, F. A., Datta, N., Singanusong, R., & CHEN, S. S. (2004) · Plant Foods for Human Nutrition · doi:10.1007/s11130-004-0049-7 · Cited by 1,561
A psychometric evaluation of the Beck Depression Inventory–II.
Dozois, D. J. A., Dobson, K. S., & Ahnberg, J. L. (1998) · Psychological Assessment · doi:10.1037/1040-3590.10.2.83 · Cited by 1,517
Research works printed but not linked: 2
- World Health Organization (2017) Depression and other common mental disorders: Global health estimates. World Health Organization, Geneva
- Alteheld B, Scheid L, Stehle P et al (2012) Kinetics of L-theanine uptake and metabolism in healthy participants are comparable after ingestion of L-theanine via capsules and green tea. J Nutr 142(12):2091–2096 · DOI · Paper page
Cited by
Sorted by citations
Potential Bioactive Components and Health Promotional Benefits of Tea ( Camellia sinensis )
Samanta, S. (2020) · Journal of the American Nutrition Association · doi:10.1080/07315724.2020.1827082 · Cited by 150
Focusing on the recent progress of tea polyphenol chemistry and perspectives
Li, S., Zhang, L., Wan, X., Zhan, J., & Ho, C. (2022) · Food Science and Human Wellness · doi:10.1016/j.fshw.2021.12.033 · Cited by 100
Green and white teas as health-promoting foods
Hinojosa-Nogueira, D., Pérez-Burillo, S., Pastoriza, S., & Rufián‐Henares, J. Á. (2021) · Food & Function · doi:10.1039/d1fo00261a · Cited by 95
Protein and Sport: Alternative Sources and Strategies for Bioactive and Sustainable Sports Nutrition
López-Martínez, M. I., Miguel, M., & Garcés‐Rimón, M. (2022) · Frontiers in Nutrition · doi:10.3389/fnut.2022.926043 · Cited by 90
How does the tea L-theanine buffer stress and anxiety
Wang, L., Brennan, M., Li, S., Zhao, H., Lange, K. W., & Brennan, C. (2022) · Food Science and Human Wellness · doi:10.1016/j.fshw.2021.12.004 · Cited by 80
Metadata
- Authors
- Williams, J. L., Everett, J. M., D’Cunha, N. M., Sergi, D., Georgousopoulou, E. N., Keegan, R. J., McKune, A. J., Mellor, D. D., Anstice, N., & Naumovski, N.
- Affiliations
- University of Canberra (AU)
- Commonwealth Scientific and Industrial Research Organisation (AU)
- Australian National University (AU)
- Aston University (GB)
- Corresponding author
- Naumovski, Nenad
- ORCID
- Venue
- Plant Foods for Human Nutrition
- Published
- 2019-11-22
- Volume
- 75
- Issue
- 1
- Pages
- 12-23
- ISSN
- 0033-5134 (ISSN-L)
- 0921-9668
- 1573-9104
- OpenAlex
- W2989961068
- Cited by
- 123
- References
- 67
- Citations by year
- 2026: 18 · 2025: 27 · 2024: 27 · 2023: 15 · 2022: 16 · 2021: 12 · 2020: 8
- FWCI
- 1.34
- Type
- journal article
- Language
- en
- Open access
- Locations
- Plant Foods for Human Nutrition (publishedVersion)
- PubMed (publishedVersion)
- Aston Publications Explorer (Aston University) (acceptedVersion)
- Institutional Research Information System University of Ferrara (University of Ferrara) (submittedVersion, other-oa)
- Topics
- Life Sciences › Agricultural and Biological Sciences › Food Science › Tea Polyphenols and Effects
- Health Sciences › Medicine › Complementary and alternative medicine › Medicinal Plant Extracts Effects
- Life Sciences › Neuroscience › Biological Psychiatry › Tryptophan and brain disorders
- Keywords
- theanine, green tea, stress, anxiety, dietary supplementation, stress response, mood, cognitive function, amino acids
- MeSH terms
- Amino Acids, Anxiety, Glutamates, Humans, Tea, Randomized Controlled Trials as Topic
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