L-Theanine | Research and limitations

1 detailed study records

Key findings from detailed records

Population: 30 adults without major psychiatric disorders Findings: Some sleep subscales differed from placebo. Results also included within-group changes and cognitive findings in subgroups.

Edited by LÍFSVARÐASources reviewed: 2026-09-21Updated: 2026-10-24Estimated reading time: 6 min

KNOWLEDGE RECORD

Category: Sleep and stress
Last Reviewed: 2026-09-21

Names and related search termsL-Theanine / L-Theanine / Theanine / Theanine

Study type: human intervention study.

Explore 10 papers by research question ↓

OUTCOME-SPECIFIC EVIDENCE

Scientific Evidence Profile

Assessment pending

An outcome-specific assessment has not yet been completed. This is not a finding that the ingredient is ineffective. The study records below remain available.

This profile concerns the stated outcome and population, not the ingredient as a whole. It is not a probability of benefit, a safety rating, a product efficacy rating or an indication of product adoption.

How we assess evidence

Ingredient Profile

What is it?: L-theanine is an amino-acid derivative found in tea. Chemically, it is an ethyl derivative of glutamine; it is distinct from caffeine. [1]

Sources for this profile

Compound properties and formulation properties are different. These sources do not establish the efficacy of a finished supplement.

PubChem — L-Theanine (CID 439378) Chemical identity reference. Maintained by NCBI, U.S. National Library of Medicine. Database record; not a clinical trial.

Profile sources checked: 2026-10-11

Read the evidence in context

Evidence: what was measured in the stated population or experimental model.
Inference: an interpretation connecting findings; its applicability depends on the study conditions.
Hypothesis: a proposed explanation or effect that remains to be tested.

Research Evidence · Scientific Synthesis

Why It Matters #

How should subjective changes in sleep and stress be interpreted? Check the detailed records for study conditions and use the literature map to compare other populations and outcomes.

What Was Studied #

Thirty adults without major psychiatric disorders participated in a randomized, double-blind crossover trial. Clinical assessments covered mood, sleep and cognitive tasks.[1]

What Was Found #

Some sleep subscales differed from placebo. Results also included within-group changes and cognitive findings in subgroups.[1]

What the Evidence Means #

Small sample, multiple outcomes and short duration. Not every improvement can be described as an effect versus placebo.[1]

Comparing similar populations, formulations, durations and outcomes helps identify where findings agree and where they differ.

What We Can Learn #

Distinguish “better than before intake” from “better than control.” The study does not establish treatment effects for insomnia or psychiatric disorders.

What Remains Unknown #

Further questions include reproducibility across populations and formulations, and the long-term balance of benefits and harms. Use the literature map as a starting point for these questions.

LITERATURE MAP / 10 PAPERS

Compare papers by conditions and findings.

A literature map covering different populations, outcomes and formulations. Read alongside detailed records to avoid treating one trial as the conclusion for an entire ingredient.

Selected: 2026-09-21. Bibliographic information checked against Europe PMC / PubMed. Editorial selection considered major papers and a range of populations and questions. This is not a systematic search covering all recent research.

10 RECORDS

A dash marks fields outside the bibliographic record. Use detailed records to compare findings and design records to connect mechanisms.

Research comparison table
Paper and topic	Study conditions	Findings and scope
Cognition and neurologyEffects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial.2019 NutrientsPMID 31623400 #	Study conditions Randomized, double-blind crossover trial Population 30 adults without major psychiatric disorders Dose L-Theanine 200 mg/day Duration 4 weeks per condition Outcomes Clinical assessments (depression, anxiety, sleep and cognitive tests) are grouped as primary outcomes in the Methods. Biomarkers are secondary outcomes.	Findings and scope Some sleep subscales differed from placebo. Results also included within-group changes and cognitive findings in subgroups. View findings and limitations DOI Authors Hidese S, Ogawa S, Ota M, Ishida I, Yasukawa Z, Ozeki M et al.
L-Theanine reduces psychological and physiological stress responses.2007 Biological psychologyPMID 16930802 #	Study conditions —	Findings and scope — Open original paper DOI Authors Kimura K, Ozeki M, Juneja LR, Ohira H
The deployment of intersensory selective attention: a high-density electrical mapping study of the effects of theanine.2007 Clinical neuropharmacologyPMID 17272967 #	Study conditions —	Findings and scope — Open original paper DOI Authors Gomez-Ramirez M, Higgins BA, Rycroft JA, Owen GN, Mahoney J, Shpaner M et al.
Effects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial.2011 BMC complementary and alternative medicinePMID 21338496 #	Study conditions —	Findings and scope — Open original paper DOI Authors Matsumoto K, Yamada H, Takuma N, Niino H, Sagesaka YM
Effects of L-theanine-caffeine combination on sustained attention and inhibitory control among children with ADHD: a proof-of-concept neuroimaging RCT.2020 Scientific reportsPMID 32753637 #	Study conditions —	Findings and scope — Open original paper DOI Authors Kahathuduwa CN, Wakefield S, West BD, Blume J, Dassanayake TL, Weerasinghe VS et al.
The effects of L-theanine, caffeine and their combination on cognition and mood.2008 Biological psychologyPMID 18006208 #	Study conditions —	Findings and scope — Open original paper DOI Authors Haskell CF, Kennedy DO, Milne AL, Wesnes KA, Scholey AB
The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans.2004 Human psychopharmacologyPMID 15378679 #	Study conditions —	Findings and scope — Open original paper DOI Authors Lu K, Gray MA, Oliver C, Liley DT, Harrison BJ, Bartholomeusz CF et al.
Assessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention task.2012 NeuropharmacologyPMID 22326943 #	Study conditions —	Findings and scope — Open original paper DOI Authors Foxe JJ, Morie KP, Laud PJ, Rowson MJ, de Bruin EA, Kelly SP et al.
Co-administration of l-cystine and l-theanine enhances efficacy of influenza vaccination in elderly persons: nutritional status-dependent immunogenicity.2008 Geriatrics & gerontology internationalPMID 19149835 #	Study conditions —	Findings and scope — Open original paper DOI Authors Miyagawa K, Hayashi Y, Kurihara S, Maeda A
Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together.2008 PsychopharmacologyPMID 17891480 #	Study conditions —	Findings and scope — Open original paper DOI Authors Rogers PJ, Smith JE, Heatherley SV, Pleydell-Pearce CW

The literature map is an index of research questions and references. Individual assessment of results, doses, funding and COI is limited to the detailed study records. Related reports from the same trial may be included; paper counts are not counts of independent trials.

Explore the research Study Records

Listed doses describe study conditions, not recommended intake.

Study RecordPMID 31623400

Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial.

PubMed 31623400 DOI: 10.3390/nu11102362

Authors: Hidese S, Ogawa S, Ota M, Ishida I, Yasukawa Z, Ozeki M, Kunugi H.
Journal: Nutrients
Publication year: 2019
Study design: Randomized, double-blind crossover trial
Participants: 30 adults without major psychiatric disorders
Dose and intervention: L-Theanine 200 mg/day
Duration: 4 weeks per condition
Outcomes and their role in the study: Clinical assessments (depression, anxiety, sleep and cognitive tests) are grouped as primary outcomes in the Methods. Biomarkers are secondary outcomes.
Findings: Some sleep subscales differed from placebo. Results also included within-group changes and cognitive findings in subgroups.
Limitations: Small sample, multiple outcomes and short duration. No apparent adverse events were reported during the 4-week interventions. Before-and-after changes and exploratory subgroup findings are distinct from overall placebo-controlled effects.
Funding: Taiyo Kagaku funded the study and supplied the study tablets.
Conflict of Interest: Yasukawa and Ozeki were Taiyo Kagaku employees.
Scope of source review: Primary full text checked for participants, intervention, results, limitations, funding and conflicts of interest on 2026-10-24.

Cite this page

LÍFSVARÐA. L-Theanine: How should subjective changes in sleep and stress be interpreted? Version 1.1 / Updated 2026-10-24

https://lifsvarda.com/knowledge/l-theanine/

Edited by LÍFSVARÐA (product brand).Editorial policy

Sources and updates

Hidese S, Ogawa S, Ota M, Ishida I, Yasukawa Z, Ozeki M, Kunugi H. (2019). Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial.Primary full text checked for participants, intervention, results, limitations, funding and conflicts of interest on 2026-10-24.

First published: 2026-09-21 / Version 1.1. Updated 2026-09-23: Added a research comparison table and links to design records. Source notes identify the scope of verification when the full paper has not been reviewed. Research summaries and LÍFSVARÐA’s interpretation are distinguished.

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