supplement

L-Theanine

Also known as Theanine, L-gamma-glutamylethylamide

Amino acid from tea leaves that crosses the blood-brain barrier and increases alpha-wave brain activity; promotes calm alertness without sedation, often paired with caffeine.

Reported side effects:Dry mouth (mild, judged possibly related to the product, resolved by follow-up; 28-day trial)Metallic taste (mild, judged possibly related to the product, resolved by follow-up; 28-day trial)

Be careful if: breastfeeding, pregnant, some medical situations

Suspect a side effect? Report it to the MHRA Yellow Card scheme ↗

6linked conditions

27linked studies

On this pageWhat studies found Safety Evidence Availability Outcomes & conditions →

Evidence

What the research actually shows

We link to relevant studies and leave interpretation to you and your healthcare professional.

What studies found

The headline results, condition by condition

The large figures are what the studies reported for each thing they measured. Open a card for every result.

Colour keyReported a benefitNo clear benefitUnclearPossible harmAmber is for highlights, such as where the most research is. It never means a result was good.

ADHD

4 of 7 results reported a benefit

3 studies, including a review of trials

Nothing measured this condition directly. These were measured:

Sleep efficiencyReported a benefitL-theanine improved sleep efficiency compared to baseline.1 review of trials · no comparable figure reported2 of 2 results reported a benefit2025 study ↗

No figure given: Impulse-control reaction time (possible harm); Overall thinking skills (reported a benefit); Percentage of time asleep (reported a benefit); Time awake during the night (unclear); Time to fall asleep (no clear benefit).

Every result

Anxiety

9 of 9 results reported a benefit

2 studies, including a review of trials

Stress and anxietyReported a benefitmeasurement not reportedL-theanine at 200-400 mg/day may reduce stress and anxiety compared to control in people exposed to stressful conditions.1 review of trials2020 study ↗

No figure given: Anxiety symptoms (reported a benefit).

Also measured alongside: Depression symptoms (reported a benefit); Planning and problem-solving skills (reported a benefit); Sleep quality (reported a benefit); and 1 more.

Every result

Safety

Safety and considerations

What sources report about side effects, who should be careful, and medicines to ask about first.

Reported side effects

Reported effect	How often	Basis	Sources
Dry mouth (mild, judged possibly related to the product, resolved by follow-up; 28-day trial)	unknown	Listed by PubMed corpus rows (PubMed 38758503)	Moulin et al. 2024, Neurol Ther 13(4):1135-1153 - 28-day randomised, double-blind, placebo-controlled trial of l-theanine in healthy adults with moderate stress; safety outcomes (PMC11263523)
Metallic taste (mild, judged possibly related to the product, resolved by follow-up; 28-day trial)	unknown	Listed by PubMed corpus rows (PubMed 38758503)	Moulin et al. 2024, Neurol Ther 13(4):1135-1153 - 28-day randomised, double-blind, placebo-controlled trial of l-theanine in healthy adults with moderate stress; safety outcomes (PMC11263523)

Be careful if you…

Applies to	What sources say	Sources
breastfeeding	LactMed (NIH): no information is available on theanine during breastfeeding; tea-level amounts are likely acceptable, but amounts from high-dose supplements are not necessarily appropriate, and it is probably better avoided while nursing a newborn or preterm infant (half-life about 1 hour).	Theanine - Drugs and Lactation Database (LactMed), NIH/NICHD, NBK615235, revised 2025-05-15 (PMID 40460226)
pregnant	No pregnancy-specific information found in the sources checked: LactMed has no separate pregnancy statement for theanine and the reviewed randomised trials excluded pregnancy.	Theanine - Drugs and Lactation Database (LactMed), NIH/NICHD, NBK615235, revised 2025-05-15 (PMID 40460226)Moulin et al. 2024, Neurol Ther 13(4):1135-1153 - 28-day randomised, double-blind, placebo-controlled trial of l-theanine in healthy adults with moderate stress; safety outcomes (PMC11263523)
some medical situations	The 28-day randomised trial reported no clinically relevant changes in laboratory values or vital signs; isolated mild events (fatigue, insomnia, reduced appetite) were judged not related or unlikely and resolved.	Moulin et al. 2024, Neurol Ther 13(4):1135-1153 - 28-day randomised, double-blind, placebo-controlled trial of l-theanine in healthy adults with moderate stress; safety outcomes (PMC11263523)

Sources

Theanine - Drugs and Lactation Database (LactMed), NIH/NICHD, NBK615235, revised 2025-05-15 (PMID 40460226)Moulin et al. 2024, Neurol Ther 13(4):1135-1153 - 28-day randomised, double-blind, placebo-controlled trial of l-theanine in healthy adults with moderate stress; safety outcomes (PMC11263523)

Evidence analytics

Where the evidence is concentrated

Audited published research for L-Theanine by condition. Drill into a pair page for the full breakdown.

Published research

L-Theanine: findings by condition

What this means: Bars count reported findings, not treatment effectiveness or certainty.

One study may report several findings or appear in more than one pairing. Counts do not show the size of an effect. Comparable numerical estimates are not established for this summary.

View the full data table

Published research: reported directions by pairing
Compound and condition	Findings (count)	Studies (count)	Reported results (finding counts)	How sure?
ADHD	7	3	Benefit: 4; no benefit: 1; harm: 1; unclear: 1; not recorded / unrecognised: 0	Not formally graded
Anxiety	9	2	Benefit: 9; no benefit: 0; harm: 0; unclear: 0; not recorded / unrecognised: 0	Not formally graded

Suggested uses (unproven)

Where people report using it and what trials suggest

Moderate evidenceRelaxation without sedation
Moderate evidenceAttention/focus combined with caffeine
Weak evidenceSleep quality (mild)

Where the evidence is negative

Common claims the trials do not support

No robust evidence as stand-alone treatment for anxiety disorders.
Effects on chronic stress are small and under-powered.

Amino acid from tea that promotes calm alertness; best evidence is for attention/relaxation, typically paired with caffeine.

Evidence grades reflect study quality and consistency, not marketing claims.

27studies referenced

21journals

2006–2026publication range

Ordered by strength of evidence, then result direction.

01Efficiency of Different Supplements in Alleviating Symptoms of ADHD with or Without the Use of Stimulants: A Systematic ReviewAl Shahab S, et al. · Nutrients · 2025PMID 40362791 ↗02The effects of L-theanine supplementation on the outcomes of patients with mental disorders: a systematic reviewMoshfeghinia R, et al. · BMC psychiatry · 2024PMID 39633316 ↗03Association between sleep pattern and pharmacological treatment in children with attention deficit disorder with hyperactivity: a systematic reviewRocha NS, et al. · Revista paulista de pediatria : orgao oficial da Sociedade de Pediatria de Sao Paulo · 2023PMID 37255110 ↗04Medicinal herbs for the treatment of anxiety: A systematic review and network meta-analysisZhang W, et al. · Pharmacological research · 2022PMID 35378276 ↗05The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic ReviewWilliams JL, et al. · Plant foods for human nutrition (Dordrecht, Netherlands) · 2020PMID 31758301 ↗06Safety, Tolerability and Efficacy of Drugs for Treating Behavioural Insomnia in Children with Attention-Deficit/Hyperactivity Disorder: A Systematic Review with Methodological Quality AssessmentAnand S, et al. · Paediatric drugs · 2017PMID 28391425 ↗

Show all 27 studies

07Green tea effects on cognition, mood and human brain function: A systematic reviewMancini E, et al. · Phytomedicine : international journal of phytotherapy and phytopharmacology · 2017PMID 28899506 ↗08To sleep or not to sleep: a systematic review of the literature of pharmacological treatments of insomnia in children and adolescents with attention-deficit/hyperactivity disorderBarrett JR, et al. · Journal of child and adolescent psychopharmacology · 2013PMID 24261659 ↗09Performance-enhancing effects of caffeine and L-Theanine among Iranian elite wrestlers: a focus on cognitive and specific physical performanceRazazan R, et al. · Journal of the International Society of Sports Nutrition · 2025PMID 40977612 ↗10Impact of L-theanine and L-tyrosine on markers of stress and cognitive performance in response to a virtual reality based active shooter training drillMcAllister MJ, et al. · Stress (Amsterdam, Netherlands) · 2024PMID 38975711 ↗11Use of Nutritional Supplements Based on L-Theanine and Vitamin B6 in Children with Tourette Syndrome, with Anxiety Disorders: A Pilot StudyRizzo R, et al. · Nutrients · 2022PMID 35215501 ↗12Effect of a Combination of Magnesium, B Vitamins, Rhodiola, and Green Tea (L-Theanine) on Chronically Stressed Healthy Individuals-A Randomized, Placebo-Controlled StudyNoah L, et al. · Nutrients · 2022PMID 35565828 ↗13Effects of L-theanine-caffeine combination on sustained attention and inhibitory control among children with ADHD: a proof-of-concept neuroimaging RCTKahathuduwa CN, et al. · Scientific reports · 2020PMID 32753637 ↗14Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled TrialHidese S, et al. · Nutrients · 2019PMID 31623400 ↗15Stress-Reducing Function of Matcha Green Tea in Animal Experiments and Clinical TrialsUnno K, et al. · Nutrients · 2018PMID 30308973 ↗16Anti-stress Effect of Green Tea with Lowered Caffeine on Humans: A Pilot StudyUnno K, et al. · Biological & pharmaceutical bulletin · 2017PMID 28566632 ↗17Anti-Stress, Behavioural and Magnetoencephalography Effects of an L-Theanine-Based Nutrient Drink: A Randomised, Double-Blind, Placebo-Controlled, Crossover TrialWhite DJ, et al. · Nutrients · 2016PMID 26797633 ↗18The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trialLyon MR, et al. · Alternative medicine review : a journal of clinical therapeutic · 2011PMID 22214254 ↗19Effects of combined GABA and L-theanine supplementation on sleep quality: an exploratory studyKonno H, et al. · European review for medical and pharmacological sciences · 2026PMID 41636292 ↗20Compositional Diversity and Functional Interactions of Bioactive Compounds in Japanese Green Tea: Focus on Matcha, Sencha, and GyokuroUnno K, et al. · Molecules (Basel, Switzerland) · 2026PMID 42654013 ↗21Identification of the GATA transcription factor family in tea plant (Camellia sinensis) and the characterizations in nitrogen metabolismGao Y, et al. · Plant physiology and biochemistry : PPB · 2025PMID 39987619 ↗22Uncovering the effects and mechanisms of tea and its components on depression, anxiety, and sleep disorders: A comprehensive reviewHan Z, et al. · Food research international (Ottawa, Ont.) · 2024PMID 39593401 ↗23Chiral analysis of theanine and catechin in characterization of green tea by cyclodextrin-modified micellar electrokinetic chromatography and high performance liquid chromatographyFiori J, et al. · Journal of chromatography. A · 2018PMID 29859684 ↗24L-Theanine Down-Regulates the JAK/STAT3 Pathway to Attenuate the Proliferation and Migration of Vascular Smooth Muscle Cells Induced by Angiotensin IIBen P, et al. · Biological & pharmaceutical bulletin · 2018PMID 30381668 ↗25New Functions and Potential Applications of Amino AcidsUneyama H, et al. · Advances in biochemical engineering/biotechnology · 2017PMID 27872968 ↗26Neurobiological effects of the green tea constituent theanine and its potential role in the treatment of psychiatric and neurodegenerative disordersLardner AL · Nutritional neuroscience · 2014PMID 23883567 ↗27Green TeaUnknown · Journal not indexed · 2006PMID 30000907 ↗

Search PubMed ↗View on PubChem ↗Find clinical trials ↗

Published research results

Reported results grouped by condition. Values and units are preserved as recorded; missing information is not estimated.

How to read this table

Benefit: What the trial saw happen: whether the measured outcome moved in the helpful direction in that one study (the tag on each row: “Benefit seen”, “No clear benefit”, “Possible harm” or “Unclear”). It is a study result — not advice, and not a promise it will work for you.
Evidence: Study design describes how research was conducted. It is not a formal certainty assessment.
Effect size: The result recorded in this summary. “Not reported” means the value is missing from the summary; it does not establish that the publication omitted it.

Reported direction, numerical results and study design are separate. Certainty has not been formally graded in this table.

Adhd (7 outcomes)

Published research: Adhd
What was measured	Reported findings	Result and units	Reported sample and duration	Study / source
Sleep efficiency	L-theanine improved sleep efficiency compared to baseline, but no specific numbers were provided in the abstract.Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): Not reported Follow-up: Not reported	Systematic review · 2025 Study details Efficiency of Different Supplements in Alleviating Symptoms of ADHD with or Without the Use of Stimulants: A Systematic Review. Systematic Review PMID 40362791
inhibitory control (Stop-signal reaction time)	L-Theanine showed harm (adverse effect) on inhibitory control (Stop-signal reaction time) (p = 0.053) compared with placebo in five boys (8-15 years) (~ 1 h post-dose). (p = 0.053)Possible harm	Not reported Recorded unit: Not reported	Sample (as reported): five boys (8-15 years) Follow-up: ~ 1 h post-dose	Randomised trial · 2020 Study details Effects of L-theanine-caffeine combination on sustained attention and inhibitory control among children with ADHD: a proof-of-concept neuroimaging RCT. Randomized Controlled Trial PMID 32753637
total cognition composite	L-Theanine improved total cognition composite (p = 0.040) compared with placebo in five boys (8-15 years) (~ 2 h post-dose). (p = 0.040)Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): five boys (8-15 years) Follow-up: ~ 2 h post-dose	Randomised trial · 2020 Study details Effects of L-theanine-caffeine combination on sustained attention and inhibitory control among children with ADHD: a proof-of-concept neuroimaging RCT. Randomized Controlled Trial PMID 32753637
Activity during sleep (time awake after sleep onset)	L-theanine (Suntheanine®) showed an unclear effect on Activity during sleep (time awake after sleep onset) compared with placebo; the difference versus placebo was not statistically established in 98 (six weeks).Unclear	Not reported Recorded unit: Not reported	Sample (as reported): 98 Follow-up: six weeks	Randomised trial · 2011 Study details The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Randomized Controlled Trial PMID 22214254
Sleep efficiency scores	L-theanine (Suntheanine®) improved Sleep efficiency scores compared with placebo in 98 (six weeks).Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): 98 Follow-up: six weeks	Randomised trial · 2011 Study details The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Randomized Controlled Trial PMID 22214254
Sleep latency	L-theanine (Suntheanine®) did not significantly improve Sleep latency compared with placebo; the difference versus placebo was not statistically established in 98 (six weeks).No clear benefit	Not reported Recorded unit: Not reported	Sample (as reported): 98 Follow-up: six weeks	Randomised trial · 2011 Study details The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Randomized Controlled Trial PMID 22214254
Sleep percentage	L-theanine (Suntheanine®) improved Sleep percentage compared with placebo in 98 (six weeks).Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): 98 Follow-up: six weeks	Randomised trial · 2011 Study details The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Randomized Controlled Trial PMID 22214254

Anxiety (9 outcomes)

Published research: Anxiety
What was measured	Reported findings	Result and units	Reported sample and duration	Study / source
reduction of stress and anxiety	L-theanine at 200-400 mg/day may reduce stress and anxiety compared to control in people exposed to stressful conditions.Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): Not reported Follow-up: Not reported	Systematic review · 2020 Study details The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review. Systematic Review PMID 31758301
Executive function	Executive function scores improved after four weeks of L-theanine vs placebo in 30 people (p=0.031). (p = 0.031)Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): 30 Follow-up: four weeks	Randomised trial · 2019 Study details Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Randomized Controlled Trial PMID 31623400
Letter fluency (lower half subgroup)	Letter fluency increased in lower-performing individuals after four weeks of L-theanine vs placebo (p=0.002). (p = 0.002)Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): 30 Follow-up: four weeks	Randomised trial · 2019 Study details Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Randomized Controlled Trial PMID 31623400
Pittsburgh Sleep Quality Index	Sleep quality scores decreased after four weeks of L-theanine vs placebo in 30 people (p=0.013). (p = 0.013)Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): 30 Follow-up: four weeks	Randomised trial · 2019 Study details Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Randomized Controlled Trial PMID 31623400
PSQI subscale: sleep latency, sleep disturbance, use of sleep medication	Sleep latency, disturbance, and medication use reduced after four weeks of L-theanine vs placebo in 30 people (p<0.05). (all p < 0.05)Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): 30 Follow-up: four weeks	Randomised trial · 2019 Study details Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Randomized Controlled Trial PMID 31623400
Self-rating Depression Scale	Depression scores decreased after four weeks of L-theanine vs placebo in 30 people (p=0.019). (p = 0.019)Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): 30 Follow-up: four weeks	Randomised trial · 2019 Study details Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Randomized Controlled Trial PMID 31623400
State-Trait Anxiety Inventory-trait	Anxiety scores decreased after four weeks of L-theanine vs placebo in 30 people (p=0.006). (p = 0.006)Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): 30 Follow-up: four weeks	Randomised trial · 2019 Study details Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Randomized Controlled Trial PMID 31623400
Verbal fluency	Verbal fluency scores improved after four weeks of L-theanine vs placebo in 30 people (p=0.001). (p = 0.001)Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): 30 Follow-up: four weeks	Randomised trial · 2019 Study details Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Randomized Controlled Trial PMID 31623400
Verbal fluency (lower half subgroup)	Verbal fluency increased in lower-performing individuals after four weeks of L-theanine vs placebo (p=0.002). (p = 0.002)Benefit seen	Not reported Recorded unit: Not reported	Sample (as reported): 30 Follow-up: four weeks	Randomised trial · 2019 Study details Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Randomized Controlled Trial PMID 31623400

Important: This page reflects observational, aggregate-only community reporting and independent published research. It is not medical advice, and it does not claim any compound treats, cures, or is effective for any condition. Always consult a qualified healthcare professional before starting, stopping, or changing any supplement or treatment.

Outcomes & conditions

Why people look into L-Theanine — and what they report

Associated conditions and community-reported outcomes, wrapped together on one page. Aggregates appear only once enough reports arrive.

Outcomes & conditions →

Availability

Where to get L-Theanine (UK)

How this compound is sold in the UK, and where our readers typically find it.

Retailer search links — we may earn commission on purchases at no cost to you. Commission never affects our evidence ratings.

Search L-Theanine on Amazon UK →Search L-Theanine on Holland & Barrett →Search L-Theanine on iHerb →