L-Theanine
SupplementThe discrepancy is explained by the medical assessment accounting for the GRADE rating of "low to very low" for monotherapy effects [s8], while the community subjectively perceives stronger and more reliable effects [c1, c2]. Community perception may reflect the combination effect with caffeine, which is better supported by clinical evidence [s2].
Unlock full information
Dosages, side effects, studies and more — free after registration.
Register for freeRating Scales
TL;DR
L-Theanine is best supported in combination with caffeine (2:1 ratio) — meta-analyses across 50 RCTs show consistent small-to-moderate effects on attention and mood (SMD 0.20–0.48). As a standalone supplement, GRADE evidence remains low to very low, which puts the strong community reports on anxiety and sleep into perspective. The safety profile is excellent (GRAS status, up to 1,200 mg/day in studies without serious adverse events), and the main caveat is a legal grey zone for synthetic L-theanine in the EU. If you drink caffeine, this is a well-justified add-on — as a solo relaxation supplement, the evidence is thin but the risk is negligible.
Description
Non-proteinogenic amino acid from green tea with demonstrated effects on relaxation, alpha-wave activity, and – in combination with caffeine – cognitive performance [s1, s2].
L-Theanine is a non-proteinogenic amino acid naturally occurring in tea leaves (Camellia sinensis) and responsible for the characteristic umami taste of green tea [s1]. As a dietary supplement, it is primarily available as a synthetic isolate or standardized tea extract, with both forms showing comparable bioavailability [s3]. Oral bioavailability is estimated at over 47–54% of the ingested amount [s3]. L-Theanine crosses the blood-brain barrier and exerts central effects on multiple neurotransmitter systems [s1]. Clinical studies have investigated the following primary areas of effect: relaxation without sedation (demonstrated by EEG alpha-wave increase) [s1], anxiety and stress reduction [s4, s5], sleep quality [s6, s7], and cognitive performance, particularly in combination with caffeine [s2, s8]. Overall, the evidence base is moderate: consistent effects on attention and mood have been demonstrated for the L-theanine + caffeine combination [s2]. For L-theanine as monotherapy, the evidence is rated low to very low according to GRADE assessment, primarily due to small sample sizes and study heterogeneity [s8]. The safety profile is well documented and considered favorable at common doses (50–400 mg) [s1, s5].
Legal Status (DE)
In Germany and the EU, synthetic L-theanine as an isolated active ingredient in dietary supplements is legally contested. The BfR and the OLG Hamburg (judgment of 22.11.2021, 3 U 46/21) classify isolated L-theanine as a novel food (Novel Food) under Regulation (EU) 2015/2283, for which no EU authorization as a novel food has yet been granted. An authorization application with the European Commission has been pending since 2024. L-theanine derived from tea extracts (Camellia sinensis) may under certain conditions be considered non-novel, provided that relevant consumption prior to May 1997 can be demonstrated. Commercially available L-theanine products exist in a legal grey area; a definitive resolution is still pending [s11, s12].
Mechanism of Action
{'source_ids_mechanismus_update': {'note': 'The GABA elevation, NMDA/AMPA antagonism, and monoamine data (serotonin, dopamine) should in future reference s13 (Nathan 2006) and s14 (Yokogoshi 1998) instead of s9 (Neurolab GmbH).', 'replace_s9_with': ['s13', 's14']}}
Dosing
Entspannung und Stressreduktion (Monotherapie)
- Dose
- 100–200 mg
- Frequency
- 1–2× täglich nach Bedarf
- Route
- oral
- Duration
- fortlaufend oder situativ
- Timing
- For acute needs 30–60 minutes before the stressful situation
- With food
- optional
Kognitive Leistung und fokussierte Aufmerksamkeit (mit Koffein)
- Dose
- 200 mg L-theanine + 50–100 mg caffeine
- Frequency
- 1× täglich morgens oder bei Bedarf
- Route
- oral
- Duration
- situativ
- Timing
- In the morning or 30 minutes before cognitively demanding tasks
- With food
- optional
Schlafqualität
- Dose
- 200–400 mg
- Frequency
- 1× täglich abends
- Route
- oral
- Duration
- fortlaufend
- Timing
- 30–60 minutes before bedtime
- With food
- optional
Schlafqualität bei Kindern mit ADHS
- Dose
- 400 mg daily (2× 200 mg)
- Frequency
- morgens und mittags
- Route
- oral
- Duration
- 6 Wochen (Studiendauer)
- Timing
- Morning and midday, not in the evening (no sedation)
- With food
- empfohlen
In human studies, single doses up to 900 mg and daily doses up to 1200 mg have been used without serious adverse effects [s5]. The FDA considers L-theanine GRAS (Generally Recognized As Safe) in the United States. No officially established UL exists for the EU; the BfR has not published a maximum amount recommendation for L-theanine in dietary supplements. Commonly used doses range from 100–400 mg daily [s1, s5].
For the L-theanine + caffeine combination, a 2:1 ratio (theanine:caffeine) is most frequently investigated in the literature [s2, s8]. Synthetic L-theanine and tea extract-based theanine show comparable pharmacokinetics [s3].
Side Effects
| Side Effect | Frequency | Severity |
|---|---|---|
| Kopfschmerzen Occasionally reported in clinical studies and community reports, particularly at higher doses [s5, c4]. | gelegentlich | leicht |
| Schwindel Rarely reported in studies; possibly due to blood pressure-lowering effects in susceptible individuals [s5, s10]. | selten | leicht |
| Magenverstimmung, Übelkeit Gastrointestinal complaints possible in sensitive individuals [s5]. | selten | leicht |
| Blutdruckabfall (Hypotonie) L-theanine may exert blood pressure-lowering effects; theoretical risk in pre-existing hypotension or combination with antihypertensive medications [s10]. | theoretisch | moderat |
| Milde Tagesmüdigkeit oder Sedierung Occasionally reported at higher doses (≥400 mg) or in sensitive individuals, although L-theanine is typically non-sedating [s1, c4]. | selten | leicht |
Contraindications
L-theanine may lower blood pressure and cause dizziness or syncope in pre-existing hypotension [s10].
Additive blood pressure-lowering effect possible; consultation with the treating physician is recommended [s10].
Insufficient safety data available for pregnancy and lactation; use not recommended [s5].
Safety data for younger children are lacking; the only RCT in children studied boys aged 8–12 years [s7].
Interactions
Synergistic
Synergistic effect on attention, reaction time, and mood; L-theanine attenuates the anxiogenic and cardiovascular side effects of caffeine. Optimal ratio 2:1 (theanine:caffeine) [s2, s8].
The combination of L-theanine and ashwagandha acts complementarily on stress and anxiety – L-theanine through rapid GABAergic and serotonergic modulation, ashwagandha through profound cortisol regulation. Together they may improve cognitive performance under stress.
L-theanine in combination with citicoline pairs well in a nootropic stack – theanine promotes calm focus, citicoline supports acetylcholine metabolism and memory performance.
L-theanine and apigenin may jointly promote sleep quality – apigenin via GABA-A receptor binding and L-theanine by promoting relaxed wakefulness prior to sleep.
The combination of L-theanine and glycine may improve sleep quality and relaxation. Glycine lowers core body temperature and promotes deep sleep, while L-theanine has a calming effect and facilitates sleep onset.
L-theanine and lion's mane are frequently combined in nootropic stacks. L-theanine provides calm focus, while lion's mane supports long-term cognitive health and neuronal regeneration.
Bacopa monnieri and L-theanine complement each other in cognitive support – Bacopa improves memory and protects against free radicals, L-theanine promotes relaxed focus.
L-theanine and Rhodiola rosea are combined in nootropic stacks for improved mental energy and stress resilience. Rhodiola reduces mental fatigue, L-theanine provides calm focus.
L-theanine and Alpha-GPC complement each other in a nootropic stack – Alpha-GPC supplies choline for acetylcholine synthesis, while L-theanine promotes calm alertness and relaxed focus. The combination may support cognitive performance and memory.
L-Theanine and L-tyrosine in combination may support focus, mood, and mental energy. L-tyrosine promotes dopamine and noradrenaline synthesis, while L-theanine provides balanced alertness.
L-Theanine combined with B vitamins (B6, B9, B12) may support cognitive function. B vitamins are essential for neurotransmitter metabolism, which L-theanine complementarily modulates.
L-Theanine and inositol may jointly support mood and anxiety reduction. Both substances influence serotonergic and GABAergic signaling pathways and may act complementarily on anxiety and mood.
L-Theanine and phosphatidylserine are combined in cognitive stacks. Phosphatidylserine supports neuronal membrane integrity and cortisol regulation; L-theanine promotes relaxed alertness and stress reduction.
Caution
Additive blood pressure-lowering effect possible; increased risk of hypotension [s10].
Theoretical potentiation of sedative effects via GABAergic modulation; avoid as a precaution [s1, s5].
Possible potentiation of serotonergic effects due to L-theanine-mediated serotonin modulation; caution and medical consultation recommended [s9].
L-Theanine may attenuate stimulant effects; interaction possible, clinical data lacking [s1].
Studies
Tier A — High Evidence
Outcome: Cognitive performance (L-theanine monotherapy)
Effect Size: GRADE evidence: low to very low; weak or inconsistent effects
Outcome: Sleep quality under L-theanine
Effect Size: Moderately positive effects; further well-controlled studies required
Outcome: Cognition, mood, and sleep in healthy adults (L-theanine, tea, L-theanine + caffeine)
Effect Size: L-theanine + caffeine vs. placebo: attention SMD 0.20–0.48; mood SMD 0.26; moderate to small effects
Tier B — Moderate Evidence
Outcome: Anxiety and stress parameters in healthy adults (200 mg/day)
Effect Size: Significant reduction in anxiety symptoms; p < 0.05
Outcome: Safety, dosing, and effects of L-theanine
Effect Size: Up to 1200 mg/day without serious adverse effects
Outcome: Sleep quality in boys with ADHD (400 mg/day)
Effect Size: Significantly higher sleep efficiency and less nocturnal awakening (actigraphy)
Tier C — Low Evidence
Outcome: Bioavailability of L-theanine from capsules vs. green tea
Effect Size: Bioavailability >47–54%; comparable kinetics between dosage forms
Community Evidence
Top reported benefits
- Relaxation and anxiety reduction without sedation
- Improved sleep quality (especially in combination with magnesium)
- Focused attention in combination with caffeine
- Reduction of caffeine-induced nervousness and palpitations
- Positive effect on withdrawal symptoms (e.g., kratom withdrawal)
Top reported issues
- No perceptible effects in some users (brand-dependent)
- Occasional headaches or mood swings
- Quality differences between products from various manufacturers
Isolated reports of adverse reactions (headaches, increased anxiety, mood fluctuations) in a subset of users [c4, c5]. One user reported that effective doses were only achieved at 10–15 g, which is substantially above typical supplement doses and should be viewed with skepticism [c1]. Quality variations between brands are frequently discussed; users recommend products with a discernible tea odor as a quality indicator [c3].
Scientific Sources
- l-theanine: From tea leaf to trending supplement – does the science match the hype for brain health and relaxation?
Mancini E, Beglinger C, Drewe J, et al. (2024). NutritionBDOI - Theanine: Health Benefits, Side Effects, Uses, Dose & Precautions (RxList)
RxList Editorial (2023). RxListBLink - Novel Food Application Summary – L-Theanine (Application 2024-15277)
European Commission, DG SANTE (2024). European Commission – Food Safety PortalALink - OLG Hamburg, Urt. v. 22.11.2021, 3 U 46/21 – Novel Food Einordnung L-Theanin
OLG Hamburg (2021). Juristische Fachdatenbank / omsels.infoALink - The neuropharmacology of L-theanine (N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent
Nathan PJ, Lu K, Gray M, Oliver C (2006). Journal of Herbal PharmacotherapyCPMID:17182482DOI - Effect of theanine, r-glutamylethylamide, on brain monoamines and striatal dopamine release in conscious rats
Yokogoshi H, Kobayashi M, Mochizuki M, Terashima T (1998). Neurochemical ResearchCPMID:9566605DOI - Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of Randomized Controlled Trials
Williams JL, Everett JM, D'Cunha NM, et al. (2024). Nutrition ReviewsADOI - Kinetics of L-Theanine Uptake and Metabolism in Healthy Participants Are Comparable after Ingestion of L-Theanine via Capsules and Green Tea
Türközü D, Şanlier N, Kocaadam B, et al. (2022). Journal of NutritionADOI - Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial
Hidese S, Ogawa S, Ota M, et al. (2019). NutrientsAPMID:31623400DOI - The effects of l-theanine on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial
Lyon MR, Kapoor MP, Juneja LR (2011). Alternative Medicine ReviewAPMID:22214254 - Examining the effect of L-theanine on sleep: a systematic review
Rao TP, Ozeki M, Juneja LR, et al. (2024). PubMed (ahead of print)APMID:41176609 - The effects of l-theanine on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial
Lyon MR, Kapoor MP, Juneja LR (2011). Alternative Medicine ReviewAPMID:22214254 - 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
Nobre AC, Rao A, Owen GN, et al. (2025). PMC / PROSPERO CRD42024575122ALink - L-Theanin: Aminosäure – Ruhe & Fokus (Neurolab Fachverzeichnis)
Neurolab GmbH (2023). Neurolab GmbH FachverzeichnisBLink
Community Sources
Storage
Unopened
Store dry, cool, and at room temperature; protect from direct sunlight and moisture.
Opened
Keep container tightly closed; protect powder form particularly from moisture.
Notes
No special storage requirements known; standard conditions for amino acid dietary supplements apply.