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Lth9.0
L-Theanine Research
Likely helpsHigh safety
35 peer-reviewed studies
What the evidence says
Likely helps
L-Theanine appears to help in 4 of 5 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 2007–2026 with a typical study size of 29 participants.
Based on 35 studies · 4 meta-analyses · 22 RCTs · 2,349 total participants
Confidence
High
What the studies found
4helped1unclear· 30 more without graded effect data
By outcome
Anxiety & stressReduced anxiety without sedation · 30-60 minutes · Calmer stress response without sedation · 30-60 minutes (acute)
Likely helps29 studies
Cognitive functionSynergistic with caffeine for improved working memory · 30-60 minutes
26 studies in the last 5 years · Latest meta-analysis: 2025
200720162026
1Sleep outcomesMeta-AnalysisCited 7×n=897 · large study2025
The findings indicate the potential use of L-theanine in the management of sleep disturbances; however, the lack of studies on "pure" L-theanine warrants further investigation.
Bulman A et al. · Sleep medicine reviews (2025)
The findings indicate the potential use of L-theanine in the management of sleep disturbances; however, the lack of studies on "pure" L-theanine warrants further investigation.
Future studies are needed to determine the adequate dose and duration of L-theanine supplementation for improving and maintaining sleep quality in healthy and clinical populations.
4Anxiety symptoms (HAMA scores)Meta-AnalysisCited 48×n=29 · very small study2022
Medicinal herbs may be promising for the treatment of anxiety.
Zhang W et al. · Pharmacological research (2022)
Noticeable benefit
← WorseNo effectBetter →
Kava was found to be an effective anxiolytic (MD: -2.46, 95% CrI: -4.47 to -0.32) but possibly ineffective in patients with generalized anxiety disorder (MD: -0.17, 95% CrI: -2.55 to -1.97).
Ginkgo biloba (MD: -4.63, 95% CrI: -9.01 to -0.23) and Withania somnifera (MD: -4.90, 95% CrI: -9.70 to -0.17) were efficacious, as measured by HAMA scores but the trials were limited by their small sample sizes.
Conversely, although Passionflower (MD: -4.20, 95% CrI: -8.82 to 0.16) and Saffron (MD: -2.71, 95% CrI: -6.06 to 0.57) did not reduce HAMA scores significantly in the summary network, both were worthy of further study because of support from separate networks.
5Cancer prevention and suppressionSystematic ReviewCited 17×2021
Further studies are necessary to ascertain the effectiveness of theanine on the prevention and suppression of cancer and shed light upon the attributable mechanisms in the in vivo condition.
Shojaei-Zarghani S et al. · Phytotherapy research : PTR (2021)
The in vivo studies also supported the potential impacts of theanine on cancer incidence or progression.
Theanine exerted its anticancer function by inhibiting EGFR, VEGFR, Met, and Akt/mTOR, JAK2/STAT3, and ERK/NFκB pathways, as well as activating the intrinsic apoptosis pathway and caspase-independent programmed cell death.
In conclusion, the results indicated moderate apoptotic, antimetastatic, antimigration, and anti-invasion effects, along with the mild antiproliferative influence of theanine on cancer.
6Systematic ReviewCited 10×n=11 · very small study2024
The findings from this systematic review suggest that LT supplementation significantly reduced psychiatric symptoms more effectively than control conditions in individuals with schizophrenia, anxiety disorders, and ADHD.
Moshfeghinia R et al. · BMC psychiatry (2024)
The findings from this systematic review suggest that LT supplementation significantly reduced psychiatric symptoms more effectively than control conditions in individuals with schizophrenia, anxiety disorders, and ADHD.
However, further studies are essential to validate these findings, deepen the understanding of the observed effects, and explore the mechanisms underlying these associations.
7Cognitive function and mood effectsSystematic ReviewCited 120×n=21 · very small study2017
The reviewed studies presented evidence that green tea influences psychopathological symptoms (e.g. reduction of anxiety), cognition (e.g. benefits in memory and attention) and brain function (e.g. activation of working memory seen in functional MRI).
Mancini E et al. · Phytomedicine : international journal of phytotherapy and phytopharmacology (2017)
The reviewed studies presented evidence that green tea influences psychopathological symptoms (e.g. reduction of anxiety), cognition (e.g. benefits in memory and attention) and brain function (e.g. activation of working memory seen in functional MRI).
The effects of green tea cannot be attributed to a single constituent of the beverage.
This is exemplified in the finding that beneficial green tea effects on cognition are observed under the combined influence of both caffeine and l-theanine, whereas separate administration of either substance was found to have a lesser impact.
8Stress and anxiety levelsSystematic ReviewCited 63×2020
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.
Williams JL et al. · Plant foods for human nutrition (Dordrecht, Netherlands) (2020)
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.
Further high-quality trials using objective measures, into the mechanisms underlying these effects, and among those with clinical insomnia would provide further useful insights.
Cotter J et al. · Nutritional neuroscience (2025)
Retrieved articles were independently reviewed by three authors.Results: Thirteen eligible trials (n = 550) that examined the effect of L-theanine (50-900 mg/day) as a standalone intervention on sleep-related outcome measures were identified.
This included two single-arm, open-label trials and eleven randomised controlled trials.Discussion: Based on the current evidence, supplementation with 200-450 mg/day of L-theanine appears to be a safe and effective way to support healthy sleep in adults.
Among the included trials, beneficial effects were reported on both objective and participant-reported outcomes, including measures linked to sleep latency, maintenance and efficiency, perceived sleep satisfaction and feelings of refreshment and recovery on waking.
11Meta-AnalysisCited 95×n=11 · very small study2014
Moderator analysis of caffeine and L-theanine doses revealed trends toward greater change in effect size for caffeine dose than for L-theanine dose, particularly during the first hour postdose.
Camfield DA et al. · Nutrition reviews (2014)
Evidence of moderate effect sizes in favor of combined caffeine and L-theanine in the first 2 hours postdose were found for outcome measures Bond-Lader alertness, attentional switching accuracy, and, to a lesser extent, some unisensory and multisensory attentional outcomes.
Moderator analysis of caffeine and L-theanine doses revealed trends toward greater change in effect size for caffeine dose than for L-theanine dose, particularly during the first hour postdose.
Standardized mean differences between placebo and treatment groups are presented for each study and outcome measure.
Further studies with a larger number participants are warranted to support these findings.
Thiagarajah K et al. · Nutrients (2022)
The supplement prolonged the total sleeping time by 45 min in the supplement receiving group compared to the placebo group (p < 0.001).
However, only sleep duration and sleep habitual efficiency showed a profound effect in both analyses (p < 0.05).
In conclusion, being given its beneficial effects without notable adverse events, it would be advantageous to use these nutraceutical ingredients to promote better sleep quality.
14Sleep onset latencyRCTCited 21×n=9 · very small study2023
Data demonstrate that using the proposed blend of novel nutritional ingredients during free living conditions reduced sleep onset latency, increased total sleep duration, and increased sleep efficiency, leading to reduced perceptions of morning sleepiness.
Langan-Evans C et al. · Medicine and science in sports and exercise (2023)
Noticeable benefit
← WorseNo effectBetter →
Likely real
The intervention trial reduced sleep onset latency (-24 ± 25 min; P = 0.002), increased total sleep time (22 ± 32 min; P = 0.01), and increased sleep efficiency (2.4% ± 3.9%; P = 0.03), while also reducing morning sleepiness ( P = 0.02).
Throughout the study, 75% of participants remained blinded to sleep assessment as a primary outcome measure, with 56% subjectively indicating improved sleep during the intervention trial.
Data demonstrate that using the proposed blend of novel nutritional ingredients during free living conditions reduced sleep onset latency, increased total sleep duration, and increased sleep efficiency, leading to reduced perceptions of morning sleepiness.
This study suggests the possibility of personalizing sleep-support supplementation based on personal life habits, sleep conditions, and sleep problems, in addition to the known efficacy of dietary supplements.
Imafuku F et al. · Nutrients (2023)
All the tested supplements were found to ameliorate sleep problems significantly (Analysis 1).
In Analysis 2, the PCs specific to improved subjects were found to differ depending on the dietary supplements and sleep problems.
In addition, subjects who consumed dairy products often showed improvement in their sleep problems with all the tested supplements.
Based on these findings, it has been demonstrated in this study that the best shooting scores and cognitive performance were achieved, particularly with the combined intake of CAF and THE.
Yilmaz U et al. · Journal of the International Society of Sports Nutrition (2023)
Regarding cognitive performance evaluation through the Stroop test, during the NR task (F=4.743, P = .001, ηp2 = .653), the combined intake of CAF and THE significantly improved reaction times compared to the intake of single CAF, THE, or PLA.
During the NER (F=2.961, P < .001, ηp2 = .741), task, the combined intake of CAF and THE significantly improved error rates compared to the intake of CAF, THE, or PLA single.
Based on these findings, it has been demonstrated in this study that the best shooting scores and cognitive performance were achieved, particularly with the combined intake of CAF and THE.
The linear dose-response attentional effects we observed warrant further studies with higher doses of L-theanine.
Dassanayake TL et al. · Nutritional neuroscience (2022)
A subsequent exploratory regression showed that each 100-mg increase in dose reduces the P3b latency by 4 ms (p < 0.05).
No dose-response effect was observed in P3b amplitude, pre-attentive ERP components or reaction time.Discussion: The findings indicate L-theanine can increase attentional processing of auditory information in a dose-dependent manner.
The linear dose-response attentional effects we observed warrant further studies with higher doses of L-theanine.
This makes it a highly promising nutritional intervention strategy.
Gong J et al. · Food & function (2026)
Chronic stress-induced sleep disorders are characterized by disrupted sleep architecture and a significant reduction in slow-wave sleep (SWS).
In CUMS mice, the combination significantly improved sleep architecture by restoring the duration of SWS and enhanced sleep quality by increasing delta wave power density.
Furthermore, it modulated central neurotransmitters, notably reversing stress-induced deficits by increasing the levels of the inhibitory neurotransmitter GABA and tryptophan, a key precursor for serotonin and melatonin.
20Schizophrenia symptom improvementRCTCited 10×n=80 · small study2023
L-Theanine adjunct to risperidone safely and tolerably outperformed adjunctive placebo for schizophrenia, and promising evidence indicated its effects on primary negative symptoms, which need to be scrutinized in further studies.
Shamabadi A et al. · Psychopharmacology (2023)
L-Theanine adjunct to risperidone safely and tolerably outperformed adjunctive placebo for schizophrenia, and promising evidence indicated its effects on primary negative symptoms, which need to be scrutinized in further studies.