L-Theanine

Clinical Summary

L-Theanine (gamma-glutamylethylamide) is a non-proteinogenic amino acid found in tea leaves (Camellia sinensis, 1-3% dry weight) and certain mushrooms (Boletus badius). Not synthesized endogenously in humans.

Why it matters: One of the few supplements with consistent evidence for promoting calm focus without sedation. The L-theanine + caffeine combination is among the best-replicated nootropic synergies in the literature — multiple independent crossover RCTs confirm cognitive benefits exceeding either compound alone. It crosses the blood-brain barrier via LAT1, increases alpha wave activity (8-13 Hz) within 30-45 minutes, modulates GABA/glutamate/dopamine/serotonin, and attenuates HPA axis stress response.

Who benefits most: Anyone who drinks caffeine (the synergy is the strongest use case), people with subclinical stress/anxiety, those with sleep quality issues (not insomnia per se — it's not sedating). Well-suited for biohackers due to excellent safety profile, no tolerance, no cycling needed.

Honest assessment: The evidence base is real but built on small RCTs (most N<50). The only proper clinical anxiety trial (Sarris 2019, GAD, N=46) was negative. Aggregated sample sizes in the prior version of this file were inflated. The compound works for subclinical stress in healthy people — extrapolating to clinical psychiatric populations is not supported. The emerging gut-brain and hepatoprotection data (2024-2026) is exciting but entirely preclinical.

Key 2024-2026 updates: 56 new PMIDs. Gut microbiome is the breakout domain — a Nature Microbiology paper (PMID 41535710) showed gut bacteria produce L-theanine to regulate host BCAA catabolism. Ferroptosis inhibition is a recurring new mechanism across muscle, intestine, myocardium, and hippocampus. First dedicated cardiovascular review published. First human blood glucose response study (Japanese). Still zero data on hair, skin, bone, eyes, sex differences, or pharmacogenomics.

Indications & Evidence

Reading this table: Stars = evidence volume/quality. Type = causal relationship (see legend). BH = Bradford Hill causal strength (/9). Safety = FAERS/trial signals for THIS indication. One row = one decision.

Hard rule: Star rating cannot exceed the causal taxonomy ceiling for its Type. E.g., AHE (animal-to-human) caps at 2/5 regardless of how many animal studies exist.

Type codes: DC=Direct causation | PC=Probable | UCC=Unreplicated causal | BC=Biomarker correlation | SE=Surrogate endpoint | ME=Mechanistic extrapolation | AHE=Animal-to-human | OA=Observational | RC=Reverse causation | CF=Confounded | FA=Folk/anecdotal | NE=No evidence BH: Bradford Hill criteria met (of 9). 7-9=strong causal | 5-6=moderate | 3-4=weak | 1-2=speculative | 0=none Safety flags: -- No signals | MON Monitor (known AEs, manageable) | WARN FAERS or trial safety signal | AVOID Contraindicated for this indication

Star rating legend: 5/5 Multiple large RCTs + meta-analyses | 4/5 Several human RCTs | 3/5 Some human pilot data | 2/5 Animal data or very limited human | 1/5 None/theoretical/debunked

Note on sample sizes: Individual L-theanine RCTs are small (N=20-98). The caffeine synergy evidence is strongest because it has been replicated across multiple independent labs. The 2025 meta-analyses (PMIDs 40056718, 40314930, 41227106) pool these small studies for more robust conclusions.

Prescribing

Dosing Table

No loading required. Effects begin within 30-50 minutes. No tolerance develops. No cycling needed.

Formulation Table

Suntheanine guarantees L-isomer purity but has no proven bioavailability advantage over quality generics. The patent is a business instrument, not a quality validation — third-party tested generics perform equivalently.

Pharmacokinetics: Rapid small intestine absorption via leucine-preferring transporter. Crosses BBB via LAT1. Minimal hepatic first-pass metabolism. Renal elimination, t1/2 = 1-2 h plasma (CNS retention longer). ~70% bioavailability. Tmax = 30-50 min. Food slightly slows but doesn't reduce absorption. Not metabolized by CYP450 — no grapefruit interaction.

Condition-Specific Protocols

Stress/Anxiety Management Protocol

Evidence: 4/5 | Key PMIDs: 31623400, 26797633, 38758503

Phase 1: Initiation (Weeks 1-2)

• 200 mg once daily (AM or PM per primary need)
• Track: subjective stress (1-10 scale daily), sleep quality
• Goal: establish baseline response; acute effects within 30-50 min

Phase 2: Therapeutic (Weeks 3-8)

• 200 mg 2x/day if single dose insufficient (AM + PM)
• Track: STAI if available, or subjective 1-10 weekly
• Expected: moderate anxiety reduction (18-30% STAI decrease per Hidese 2019)

Phase 3: Maintenance (Week 8+)

• Continue effective dose indefinitely; no tolerance develops
• Reassess quarterly: still needed? Still effective?

Stop/Reassess: If no subjective benefit by week 4, L-theanine may not be effective for you. Consider: dose increase to 400 mg/day, adding Magnesium, or addressing root cause of stress.

Caffeine Synergy Protocol

Evidence: 5/5 | Key PMIDs: 18681988, 18006208, 21040626

• 100-200 mg L-theanine + 50-100 mg Caffeine (2:1 ratio)
• Take 30-60 min before cognitive demands
• Effects last 2-4 h; can repeat
• Benefits: improved attention accuracy (10-20%), reduced caffeine jitteriness, enhanced task switching
• Can stack with existing coffee habit — one cup coffee (~95 mg caffeine) + 200 mg L-theanine

Sleep Quality Protocol

Evidence: 4/5 | Key PMIDs: 40056718, 31623400, 22214254

• 200-400 mg, 30-60 min before bed
• Not sedating — works by promoting relaxation conducive to sleep
• Optional: combine with GABA 100-300 mg for enhanced sleep latency reduction (PMID 30707852)
• Expected: PSQI improvement of 2-3 points by week 4
• If ineffective alone after 2 weeks: add Magnesium glycinate 300 mg or Melatonin 0.5-3 mg

Safety

Interactions Table

No antagonistic nutrient interactions identified. L-theanine does not compete for absorption or interfere with other supplement mechanisms. Food slightly slows absorption without reducing bioavailability. Not metabolized by CYP450 — no grapefruit interaction.

Contraindications

• Absolute: None identified
• Relative: Pregnancy/lactation (insufficient safety data — avoid supplementation; dietary tea safe in moderation)

Adverse Effects (ranked by frequency)

Clinical trials: Exceptionally well-tolerated across all RCTs up to 900 mg/day. No statistically significant AE difference vs placebo.

• Uncommon (<1%): Mild headache (resolves with continued use), dizziness at very high doses (>900 mg), mild GI upset
• Rare (<0.1%): Paradoxical drowsiness in small minority, allergic reaction (no documented serious cases)
• Community-reported (anecdotal, not in trials): Vivid dreams/nightmares (~15-20% of Drugs.com reports), paradoxical anxiety increase (non-trivial minority), heart palpitations (~12% Drugs.com, likely confounded)
• NOAEL: >2000 mg/kg/day in animal studies — far exceeding human therapeutic doses
• Tolerance: Does not develop. No dependence. No withdrawal. Can stop abruptly.
• Long-term safety: Studies up to 12 months show sustained benefits without safety concerns

FAERS Signal Table

FAERS assessment: Total 572 reports mentioning theanine. Only 1 report has theanine as suspect drug (arthralgia, dry mouth, insomnia — non-serious). Zero suspect-drug reports since 2024 (0/97 recent reports). All death-outcome reports are concomitant mentions in a single polypharmacy event. No genuine safety signal detected. This is consistent with the excellent clinical trial safety profile.

Monitoring Table

L-theanine requires no laboratory monitoring. No baseline tests needed. For research/tracking purposes: subjective stress score (1-10), PSQI for sleep, cognitive task performance.

Special Populations

Renal Impairment

Disease-Specific Notes

• Celiac: Standard dosing once intestinal healing established. Verify gluten-free certification.
• Diabetes (T1/T2): No effect on blood glucose or insulin. No dose adjustment. First human glucose study (PMID 41845544, 300 mg) showed no significant glucose changes.
• Thyroid (Hashimoto's/hyper): No thyroid effects. No levothyroxine interaction. No spacing needed.
• IBD (active flare): Absorption may be reduced; standard dosing still appropriate.
• Autoimmune (RA, SLE): Safe; no documented concerns with DMARDs, biologics, or immunosuppressants.
• Cancer: Safe during treatment. Cystine+theanine combination studied in Japanese oncology for chemotherapy AE reduction (PMIDs 31811480, 32594273).
• Hepatic impairment: No dose adjustment at any Child-Pugh level (minimal hepatic metabolism).

Synergies & Stacking

No antagonistic interactions identified.

Individual Response Modifiers

Sex-Specific Considerations

No clinically significant sex-specific differences known for L-theanine. Key studies (Hidese 2019, Lyon 2011) included both sexes without reporting differential effects. The Lyon 2011 ADHD study was conducted exclusively in boys — female ADHD response data is absent. No pregnancy/lactation safety data exists for supplemental doses.

New trial recruiting (NCT07135232): L-theanine + resistance training in perimenopause/menopause — first female-specific study.

Genetic Modifiers

No known pharmacogenomic modifiers for L-theanine. The LAT1 (SLC7A5) transporter mediates BBB crossing, but no human polymorphism studies exist for L-theanine response. This remains a complete research gap.

Community & Anecdotal Evidence

Disclaimer: This section captures real-world user reports from online communities. None of this constitutes clinical evidence. N-sizes are approximate. Selection bias, placebo effect, and recall bias are inherent. Presented for completeness, not as medical guidance.

Dominant Sentiment

Positive (60-70% across platforms, ~N=2000+ reports). The caffeine+theanine stack is the most universally praised use case (~85% agreement). L-theanine is the #1 recommended starter nootropic on r/Nootropics.

However: Drugs.com user reviews paint a more divided picture: 43% positive vs 45% negative (N=154) — significantly less favorable than Reddit/biohacker communities, likely due to different population expectations (clinical relief vs optimization).

What Users Report

Community Dosing vs Clinical

Popular Stacks (Community)

Red Flags & Skepticism Notes

• MLM involvement: None detected. L-theanine is not an MLM product.
• Influencer concentration: Andrew Huberman's Momentous partnership is the main disclosure concern — he recommends L-theanine frequently with a branded product affiliation. Otherwise, recommendation is broad-based across many independent voices.
• Astroturfing signals: None detected. Community discussion appears organic.
• Commercial bias: Blog ecosystem (Examine, Selfhacked, Nootropics Expert) is structurally affiliate-biased but not fraudulent. Claims generally align with evidence.

Folk vs Clinical Reality Check

Community experience aligns unusually well with clinical data for the caffeine synergy ratio (2:1) and sleep dosing (200 mg). The main divergence: communities report vivid dreams (~15-20%) and paradoxical anxiety (~10-15%) at rates far higher than clinical trials document (trials report essentially zero AEs). This gap likely reflects: (1) trial populations are screened and homogeneous, (2) trials use standardized assessment that misses subjective dream quality, and (3) community reports capture rare responders that small trials never detect. The Drugs.com negativity bias (~45% negative) vs Reddit positivity (~70% positive) likely reflects population differences: Drugs.com users seek medical-grade relief, while Reddit users seek marginal cognitive optimization and have lower expectations to meet.

Deep Dive: Mechanisms & Research

Core mechanisms (clinically translated):

• Crosses BBB via LAT1 transporter. Weak NMDA glutamate receptor antagonist (prevents excitatory overload). Increases GABA (primary inhibitory neurotransmitter). Modulates dopamine and serotonin in striatum (PMID 18196445). Selectively increases alpha waves (8-13 Hz) without increasing theta/delta waves — relaxation without sedation.
• Upregulates SLC38A1 in neural stem cells (PMID 31952134) — potential neurogenesis pathway.

Emerging mechanisms (2024-2026, preclinical):

• Ferroptosis inhibition: Recurring new mechanism across muscle (PMID 41237995), intestine (PMID 41554461), myocardium (PMID 40328913), and hippocampus (PMID 40682446). L-theanine appears to be a broad ferroptosis modulator — potentially relevant to neurodegeneration and organ protection.
• Gut microbiome-host axis: Nature Microbiology (PMID 41535710) showed gut bacteria produce L-theanine endogenously to regulate host BCAA catabolism via BCAT2. This reframes L-theanine from purely exogenous supplement to part of the microbiome-host metabolic axis.
• Gut-brain antidepressant pathway: L-theanine alleviates depression in animal models via gut SCFA production to prefrontal cortex signaling (PMIDs 41326381, 41360561).
• Hepatoprotection: Seven new preclinical papers (2024-2026) demonstrate liver protection across alcoholic injury, ischemia-reperfusion, fibrosis, and MASLD models.

Clinical Trials (from BioMCP / ClinicalTrials.gov)

52 registered trials identified (37 completed, 8 recruiting, 2 not yet recruiting, 2 terminated, 1 unknown). Key active/recruiting:

East Asian registries: UMIN000028603, UMIN000033812, UMIN000050613, UMIN000052597 (Japan — stress, cognition, sleep).

Regulatory Status

• FDA: GRAS (GRN 000209 Suntheanine 2007; GRN 000338 Blue California). Dietary supplement under DSHEA. Not an approved drug. GRAS limit: 250 mg/serving in foods.
• EMA/EFSA: No drug approval. EFSA rejected all health claims 2011 (cognitive function, stress, sleep, menstrual discomfort). Synthetic L-theanine classified as Novel Food (authorization terminated 2022). Tea-derived = not novel.
• Japan: Approved in all foods (restricted in infant foods). FOSHU/FFC eligible. Suntheanine originated here (Taiyo International).
• Health Canada: Natural Health Product.
• Australia/NZ: Listed complementary medicine ingredient.

Ataraxia Verdict (as of 2026-04-16)

Evidence Classification (Mode 5: Evidence Classifier)

Hype Check (Mode 1: Fallacy Radar)

• Inflated N-sizes (HIGH): Prior version claimed "N=680+ for stress" and "N=400+ for sleep." Actual cited RCTs total ~115 for stress and ~130 for sleep. Aggregation creates illusion of larger evidence base.
• Hasty generalization, animal to human (HIGH): Neuroprotection, IBD, hepatoprotection, and cardiovascular claims are entirely preclinical. The file gave these extensive space, implying clinical relevance that doesn't exist yet.
• Cherry-picking (MEDIUM): Hidese 2019 (N=30, positive) is prominently featured; Sarris 2019 (N=46, negative for GAD) is de-emphasized. The positive small trial gets higher billing than the negative larger trial.
• Appeal to antiquity (MEDIUM): "Tea consumption spans millennia" conflates 20-50 mg/cup with 200-400 mg supplemental doses.
• Industry-funded prominence (MEDIUM): AlphaWave (KGK Science) and Suntheanine (Taiyo International) fund multiple cited studies. Independent replication exists but is also small-scale.

Evidence Gaps

• No large-scale RCT (>200 participants) for any indication
• No human neuroprotection trials despite extensive animal data
• No pregnancy/lactation safety data from human studies
• No pharmacogenomic studies (LAT1 polymorphisms unknown)
• No sex-specific response analysis
• No head-to-head trials vs prescription anxiolytics
• No cardiovascular RCTs
• No human IBD/gut trials despite strong preclinical signal
• Zero data on hair, skin, bone, eye health, sarcopenia
• Dose-response for sleep not systematically characterized

Bias Flags (Mode 4: First Principles)

What survives scrutiny: Alpha wave enhancement (objective EEG measurement, consistent), caffeine synergy (independent replication across labs), acute stress reduction (biomarker-confirmed). What doesn't: any claim about clinical psychiatric populations (GAD trial negative), neuroprotection (all animal), disease-specific protocols in prior file version (zero evidence for each listed condition). The "strong evidence" quality rating was generous — downgraded to "moderate-strong" reflecting the consistent but small-sample evidence base.

Manipulation Flags (Mode 2: Manipulation Shield)

• Industry marketing: Suntheanine (Taiyo International) and AlphaWave (KGK Science) fund multiple studies and promote branded forms. The 2:1 theanine:caffeine ratio is heavily promoted by combo product manufacturers. Industry involvement is transparent but creates citation bias toward branded forms.
• Influencer economics: Andrew Huberman recommends L-theanine via Momentous partnership (affiliate). This is the primary disclosure concern. No other major influencer conflicts identified.
• Counter-narrative manipulation: Minimal. L-theanine is too mild and cheap to attract pharma competitive attacks. EFSA's 2011 health claim rejection was science-based, not commercially motivated.
• Cui bono summary: PRO — Taiyo International (Suntheanine patent holder), KGK Science (AlphaWave), generic supplement companies, tea industry. ANTI — minimal; pharma anxiolytics aren't genuinely threatened by a mild amino acid. This is low-conflict territory.
• Red team highlight: The most concerning angle is evidence quality — the entire evidence base rests on RCTs with N=20-98. One well-powered negative trial (like Sarris 2019 for GAD) can overturn the positive signal. The 2025 meta-analyses partially address this by pooling, but meta-analyses of small studies amplify publication bias.

Decision Support (Mode 3: Clarity Compass)

• Health utility score: 7/10 — broad general utility given the prevalence of stress, caffeine consumption, and sleep issues; excellent safety profile and replicated caffeine-synergy evidence make it one of the easiest low-risk optimization compounds despite modest effect sizes.
• Opportunity cost: Very low. $10-30/month. No monitoring. No interactions. No cycling. One more capsule/day.
• Verdict: ADD — for the caffeine synergy use case. The evidence is real, replicated, and the risk-benefit ratio is excellent. For sleep-only use, WATCH LIST — evidence is moderate and alternatives (Magnesium, Melatonin) have stronger sleep-specific data. For everything else (neuroprotection, IBD, depression), SKIP until human data exists.

Bottom Line

L-theanine is a genuinely useful, extremely safe amino acid whose strongest evidence is for the caffeine synergy (real, replicated, worth using) and mild stress reduction in healthy people (real but modest). The evidence base is built on small trials — consistent direction but not overwhelming power. It does NOT work for clinical anxiety disorders (the one proper GAD trial was negative). The exciting 2024-2026 preclinical data on gut-brain axis, ferroptosis, and hepatoprotection is promising but zero human trials exist for these indications. At $10-30/month with essentially no risk, it's one of the easiest supplement decisions: try it, notice whether it helps, keep or drop based on subjective response.

Practical Notes

Brands & Product Selection

Quality markers: USP Verified, NSF Certified, ConsumerLab Approved, or lot-specific CoA. Suntheanine guarantees >99% L-isomer purity. Heavy metals should be <1 ppm lead, <0.1 ppm cadmium.

Red flags: No third-party testing, "cure anxiety" claims, proprietary blends hiding theanine content, <$5/month for 200 mg/day, no manufacturer contact info.

Reputable options (not endorsements): Thorne (Suntheanine, NSF), NOW Foods (USP, value), Doctor's Best (Suntheanine), Jarrow Formulas (Suntheanine), Pure Encapsulations (hypoallergenic).

Storage & Handling

Room temperature (15-25C). Protect from direct sunlight. Keep dry (moisture causes clumping). Shelf life 2-3 years unopened, 18-24 months after opening.

Palatability & Compliance

Nearly tasteless to slightly umami. Powder dissolves well in water. Capsules more convenient. Compatible with all beverages — especially good in coffee (built-in caffeine synergy). No masking needed. Habit stack: take with morning coffee for cognitive benefit, or with evening routine for sleep.

Exercise & Circadian Timing

• Pre-workout: 200 mg 30-60 min before training may reduce exercise-induced stress response. New data: caffeine+theanine improved cognitive and physical performance in elite wrestlers (PMID 40977612).
• Post-workout: No specific recovery benefits identified.
• AM: Best for cognitive enhancement with caffeine.
• PM: Best for sleep quality — does NOT cause drowsiness, promotes relaxation.
• Flexible: Can be taken any time; no circadian restrictions. No accumulation.

Cost

Best value: generic from third-party tested brand. Premium: Suntheanine for guaranteed quality.

What We Don't Know

• No large-scale RCT (>200 participants) for any indication — the entire evidence base is small trials
• Whether the positive small-trial signal would survive a well-powered study (Sarris 2019 suggests maybe not for clinical populations)
• Optimal dose-response for sleep (200 vs 400 mg, with or without GABA)
• Whether the exciting gut-brain, ferroptosis, and hepatoprotection preclinical data translates to humans at all
• Pharmacogenomic modifiers (LAT1 variants, others) — complete gap
• Sex-specific response differences — no data
• Long-term (>12 month) safety from RCTs at supplemental doses
• Pregnancy/lactation safety beyond dietary tea consumption
• Whether vivid dreams and paradoxical anxiety (reported by ~10-20% of community users) are real phenomena or confounded
• Hair, skin, bone, eye health effects — zero data in any direction
• Cardiovascular outcomes in humans — only animal data despite new dedicated CVD review
• How the Nature Microbiology finding (gut bacteria produce endogenous L-theanine) changes the supplementation calculus

References

Systematic Reviews & Meta-Analyses (2024-2026)

• PMID 41227106 | 2025 | L-theanine on cognitive performance: SR+MA of RCTs
• PMID 41176609 | 2026 | Cotter J | L-theanine supplementation trials on sleep: SR
• PMID 40314930 | 2025 | Payne ER | Tea/L-theanine/caffeine on cognition, sleep, mood: SR+MA
• PMID 40056718 | 2025 | Bulman A | L-theanine on sleep outcomes: SR+MA
• PMID 40722728 | 2025 | Cavanah AM | Green tea bioactives on mood and BDNF: SR of RCTs
• PMID 40362791 | 2025 | Al Shahab S | Supplements for ADHD symptom alleviation: SR
• PMID 39633316 | 2024 | Moshfeghinia R | L-theanine in mental disorders: SR
• PMID 39854799 | 2025 | Dashwood R | Critical review: does L-theanine brain health science match hype?

Systematic Reviews (pre-2024)

• PMID 31758301 | 2020 | Williams JL | L-theanine for stress/anxiety: SR
• PMID 28899506 | 2017 | Mancini E | Green tea on cognition/mood/brain: SR
• PMID 25759004 | 2015 | Rao TP | Safe natural sleep aid: review (NOAEL >2000 mg/kg/day)
• PMID 26192072 | 2017 | Turkozu D | L-theanine metabolism, health effects, safety: review

Landmark RCTs

• PMID 31623400 | 2019 | Hidese S | N=30, 200 mg/day, 4-wk: STAI p=0.006, PSQI p=0.013, SDS p=0.019
• PMID 18681988 | 2008 | Owen GN | N=27, 100 mg+50 mg caffeine: attention+accuracy improved
• PMID 18006208 | 2008 | Haskell CF | Dose-dependent cognitive benefits with caffeine combo
• PMID 21040626 | 2010 | Giesbrecht T | N=44, 97 mg+40 mg caffeine: improved alertness
• PMID 26797633 | 2016 | White DJ | N=34, MEG-confirmed stress reduction
• PMID 34562208 | 2021 | Evans M | AlphaWave: frontal alpha power increase
• PMID 22214254 | 2011 | Lyon MR | N=98, ADHD boys: sleep quality improved via actigraphy
• PMID 32753637 | 2020 | Kahathuduwa CN | ADHD children: neuroimaging RCT, attention improved
• PMID 30580081 | 2019 | Sarris J | N=46, GAD: NO significant benefit vs placebo (NEGATIVE trial)
• PMID 38758503 | 2024 | Moulin M | AlphaWave 28-day: safe and efficacious for moderate stress
• PMID 33751906 | 2021 | Baba Y | Elderly 50-69: verbal fluency and executive function improved
• PMID 39213264 | 2024 | Uchida K | 12-month matcha RCT: cognitive benefits in elderly
• PMID 32777998 | 2022 | Dassanayake TL | Dose-response: 4 ms P3b latency reduction per 100 mg
• PMID 36263942 | 2023 | Dassanayake TL | Dose-response: psychomotor speed and attention

New Human Studies (2024-2026)

• PMID 40026748 | 2025 | Deshpande SS | GABA vs L-theanine for preoperative anxiety: head-to-head RCT
• PMID 39934632 | 2024 | Lim IS | L-theanine reduced cognitive anxiety + cortisol in archery (Korean)
• PMID 38975711 | 2024 | McAllister MJ | L-theanine+L-tyrosine reduced stress in VR training
• PMID 40977612 | 2025 | Razazan R | Caffeine+L-theanine in elite wrestlers (Iranian)
• PMID 40789769 | 2025 | Nawarathna GS | High-dose theanine+caffeine in sleep-deprived adults (crossover RCT)
• PMID 39052627 | 2025 | Karunaratne UW | L-theanine improved attention in sleep-deprived adults (Sri Lankan)
• PMID 41636292 | 2026 | Konno H | GABA+L-theanine combo improved sleep (Japanese)
• PMID 41845544 | 2026 | Yamaura S | First human blood glucose response to 300 mg L-theanine (Japanese)
• PMID 21208586 | 2011 | Ritsner MS | 400 mg/day adjunct in schizophrenia: reduced anxiety/activation
• PMID 37169515 | 2023 | Nematizadeh S | L-theanine+fluvoxamine in moderate-severe OCD

Key Preclinical (2024-2026)

• PMID 41535710 | 2026 | Wang Y | Gut microbiota-derived L-theanine promotes BCAA catabolism (Nature Microbiology)
• PMID 41796839 | 2026 | Garcia-Nino WR | First CVD review: L-theanine molecular targets in cardiovascular disease
• PMID 41237995 | 2026 | Huang Y | Muscle oxidative damage via mitochondria/ferroptosis
• PMID 41554461 | 2026 | Shi C | Intestinal oxidative injury via ferroptosis modulation
• PMID 40328913 | 2025 | Huang X | Myocardial protection in sleep deprivation via SIRT1/ferroptosis
• PMID 40682446 | 2025 | Huang X | Learning/memory via NOX4-ferroptosis in sleep deprivation
• PMID 40311999 | 2025 | Liu A | UC barrier repair via microbiota/SCFAs
• PMID 39197065 | 2024 | Xu W | UC via gut microbiota MHC-II dependent mechanism
• PMID 41326381 | 2025 | Peng Y | Depression via gut-SCFA-brain axis
• PMID 41886951 | 2026 | Zuo G | EGCG+L-theanine for obesity/MASLD
• PMID 38893565 | 2024 | Chen L | Lifespan extension in C. elegans
• PMID 41410739 | 2025 | Kawada K | SLC38A1-mediated neuroblastoma growth inhibition (Japanese)

Mechanistic Studies

• PMID 18196445 | 2009 | Yamada T | Neurotransmitter modulation in striatum
• PMID 31952134 | 2020 | Yoneda Y | SLC38A1 upregulation in neural stem cells
• PMID 34988886 | 2022 | Chen CN | Neuroprotection in Parkinson's rat model
• PMID 32720164 | 2020 | Chen L | IBD protection in rat model (NF-kB/MAPK)
• PMID 30707852 | 2019 | Kim S | GABA+theanine sleep latency/NREM (animal)
• PMID 38583116 | 2024 | Yamaura S | Pharmacokinetics in mice (70% bioavailability)
• PMID 26957301 | 2017 | Jamwal S | Neuroprotection via NO pathway modulation