PMID 42410082 Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials Meta-analysis · Mol Psychiatry, 2026 31 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s, 1,168 people - a single 200 mg dose 30–60 min before testing significantly improved choice reaction time (SMD 0.51); stress reduction was small (SMD 0.31) and driven by biased studies.
Key summary
A recent meta-analysisA statistical synthesis combining results of multiple studies into one conclusion. pooling 31 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s (1,168 people) across healthy and clinical populations. A single 200 mg dose taken 30–60 minutes before cognitive testing significantly sped up choice reaction time (SMD 0.51), suggesting enhanced attention. By contrast, acute stress reduction was small (SMD 0.31) and largely driven by studies at high risk of bias. Excluding one outlier, depression scores fell significantly after a single dose (SMD 0.69), but the authors said confirmation in high-quality trials is needed, and anxiety effects were inconsistent. No serious adverse events occurred.
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BACKGROUND: L-theanine, an amino acid derived from green tea, has been suggested to alleviate affective symptoms and enhance cognitive performance, but its clinical relevance remains uncertain. METHODS: We conducted a systematic review and meta-analysis of 31 randomised controlled trials (n = 1168) comparing oral L-theanine with placebo in healthy and clinical populations. The primary outcome was the acute effect of a single dose on stress in healthy adults. Secondary outcomes included clinical measures (stress after repeated dosing, anxiety, depressive symptoms, and fatigue) and cognitive measures (reaction times and attention tasks with single and repeated doses). Safety was assessed by comparing dropout rates and reasons between L-theanine and placebo groups. RESULTS: A single 200 mg dose taken 30-60 min before cognitive testing significantly improved choice reaction time (Standardised Mean Difference [SMD] = 0.51; 95% CI, 0.25-0.77), indicating enhanced attention. The reduction in acute stress was modest (SMD = 0.31) and largely influenced by studies with a high risk of bias. No significant effect on fatigue was observed. Excluding one outlier, a significant reduction in depressive symptoms following a single dose in healthy individuals was found (SMD = 0.69; 95% CI, 0.13-1.25) with low heterogeneity. Anxiety effects were inconsistent and non-significant except for one study on psychotic anxiety (SMD = 0.54; 400 mg/day for 8 weeks). No serious adverse events were reported. CONCLUSIONS: L-theanine is safe and shows a robust short-term benefit on attention in healthy adults, with a potential antidepressant effect warranting confirmation in high-quality trials, especially in clinical populations. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.
View original ↗ PMID 40314930 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 Meta-analysis · Nutr Rev, 2025 (tea-company funded) 50 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s (15 meta-analyzed) - theanine plus caffeine improved cognition/mood by a small-to-moderate degree; theanine alone improved choice reaction time (SMD -0.35). CIs showed much uncertainty.
Key summary
A systematic review that screened 50 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s in healthy people and meta-analyzed 15. Theanine plus caffeine showed small-to-moderate benefits versus placeboAn inert dummy treatment used as the comparison baseline. within 1 to 2 hours for choice reaction time, attention accuracy, and overall mood, and theanine alone shortened choice reaction time (SMD -0.35). The authors noted the confidence intervals frequently revealed uncertainty about direction and magnitude. The study declares tea-company (Lipton/Unilever) funding and affiliations, so it should be read with that conflict of interest in mind.
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CONTEXT: The bioactive compounds found in tea from Camellia sinensis, namely theanine, caffeine, and polyphenols, can potentially improve short-term and long-term health outcomes. OBJECTIVE: The aim of this study was to assess the effects of tea, theanine alone, or theanine plus caffeine on cognition, mood, and sleep outcomes, using data from randomized controlled trials (RCTs) in healthy participants. DATA SOURCES: The Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, Embase, and Ovid Medline were searched up to and including August 2023. DATA EXTRACTION: Data relevant to the participants, interventions, comparisons, outcomes (ie, cognition, mood, and sleep), and study design were extracted. DATA ANALYSIS: Fifty RCTs were included in the review, of which 15 were eligible for at least 1 meta-analysis, most commonly performed by use of standardized mean differences (SMD), in random effects models. After intake of theanine plus caffeine, and of placebo, small-to-moderate differences were found between these interventions in the first hour (h1) and second hour (h2), that favoured theanine plus caffeine, with regard to cognition and mood outcomes such as choice reaction time (h1: SMD, -0.48; 95% CI, -1.01, 0.05), digit vigilance task accuracy (h2: SMD, 0.20; 95% CI, 0.02, 0.38), attention switching task accuracy (h2: SMD, 0.33; 95% CI, 0.13, 0.54), and overall mood (h2: SMD, 0.26; 95% CI,-0.10, 0.63). There was a small-to-moderate difference between the effects of theanine and placebo that favored theanine on choice reaction time (h1: SMD, -0.35; 95% CI,-0.61, -0.10). The CIs frequently highlighted the uncertainty surrounding the direction and magnitude of these differences. CONCLUSIONS: This meta-analysis provides evidence that theanine plus caffeine, and theanine alone, could be beneficial for cognitive and mood outcomes. More research using tea beverages or tea-equivalent bioactive doses and research in free-living participants is needed. PROSPERO REGISTRATION NO: CRD42022351601. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.
View original ↗ PMID 24946991 Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis Meta-analysis · Nutr Rev, 2014 11 studies - caffeine plus theanine gave moderate effects on alertness and attention-switching accuracy within 2 hours; effect size depended more on caffeine than theanine dose.
Key summary
A meta-analysisA statistical synthesis combining results of multiple studies into one conclusion. of the acute cognitive and mood effects of tea constituents (L-theanine, EGCG) alone or combined with caffeine (11 placeboAn inert dummy treatment used as the comparison baseline.-controlled studies). The caffeine plus theanine combination showed moderate effect sizes for alertness (Bond-Lader) and attention-switching accuracy within 2 hours of dosing. However, moderator analysis found the change in effect size depended more on caffeine dose than theanine dose, especially in the first hour. In other words, much of the combined alerting effect comes from caffeine.
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A systematic review and meta-analysis was conducted on 11 randomized placebo-controlled human studies of acute effects of tea constituents L-theanine and epigallocatechin gallate, administered alone or in combination with caffeine, on cognitive function and mood. The outcome measures of mood were alertness, calmness, and contentedness, derived from the Bond-Lader scales, and state anxiety, from the State-Trait Anxiety Inventory. Cognitive measures assessed were attentional switch, intersensory attention, and rapid visual information processing. Standardized mean differences between placebo and treatment groups are presented for each study and outcome measure. Meta-analysis using a random-effects model was conducted when data were available for three or more studies. 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. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.
View original ↗ PMID 31758301 The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review Systematic review · Plant Foods Hum Nutr, 2020 9 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s - 200–400 mg a day may help reduce stress and anxiety in people under stressful conditions. Longer, larger trials needed.
Key summary
A PRISMA systematic review of how pure L-theanine supplements affect human stress responses and anxiety (9 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s). The authors judged that 200–400 mg a day may help reduce stress and anxiety in people exposed to stressful conditions. They stressed that longer-term, larger clinical studies and studies of regular dietary intake are still needed. Note that this is a narrative synthesis rather than a meta-analysisA statistical synthesis combining results of multiple studies into one conclusion..
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The green tea amino acid, L-theanine (L-THE) is associated with several health benefits, including improvements in mood, cognition and a reduction of stress and anxiety-like symptoms. 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. 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. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.
View original ↗ PMID 41176609 Examining the effect of L-theanine on sleep: a systematic review of dietary supplementation trials Systematic review · Nutr Neurosci, 2026 (tobacco-company researchers) 13 trials, 550 people - 200–450 mg a day appears safe and effective for supporting healthy sleep (subjective and objective measures). Evidence in clinical insomnia is limited.
Key summary
A systematic review of how standalone L-theanine supplementation affects sleep (13 trials, 550 people, 50–900 mg a day; 11 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s and 2 open-label). The authors reported that 200–450 mg a day appears safe and effective for supporting healthy sleep in adults, with benefits on measures such as sleep latencyThe time it takes to actually fall asleep after going to bed; shorter means falling asleep faster., maintenance, efficiency, and feeling refreshed. They noted that higher-quality trials using objective measures and studies in people with clinical insomnia are still needed. The authors declare affiliation with a tobacco company (British American Tobacco), so the conflict of interest should be kept in mind.
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Objective: Sleep problems are a common complaint among adults worldwide, however, the use of prescription and over-the-counter products may not always be an appropriate or desirable solution. L-theanine is a naturally occurring, non-protein amino acid that can be found in the leaves of the tea plant Camellia sinensis. Previous studies have reported that consumption of L-theanine can help to aid relaxation, without causing sedation or adversely impacting cognitive function. Building on these calming effects and results from recent pre-clinical studies, the aim of this review was to systematically appraise the scientific literature to establish whether dietary supplementation with L-theanine can also help to support sleep in humans.Methods: Electronic database searches of Ovid MEDLINE, PsycINFO, Embase, CENTRAL and Google Scholar were conducted from inception to 3rd February 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. Further high-quality trials using objective measures, into the mechanisms underlying these effects, and among those with clinical insomnia would provide further useful insights. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.
View original ↗ PMID 31623400 Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial Crossover RCT · Nutrients, 2019 (ingredient supplier involved) Crossover RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects., 30 people - after 4 weeks of 200 mg a day, sleep-quality index (PSQI), anxiety (STAI-trait), and depression scores fell; verbal fluency and executive function improved.
Key summary
A randomized, crossover, double-blind RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects. in 30 healthy adults. After 4 weeks of 200 mg a day, sleep-quality index (PSQI), anxiety (STAI-trait), and depression scores fell, with sleep latencyThe time it takes to actually fall asleep after going to bed; shorter means falling asleep faster., sleep disturbance, and sleep-medication subscores in particular dropping versus placeboAn inert dummy treatment used as the comparison baseline.. Verbal fluency and executive function cognitive scores also improved. Interpret with the small sample and the conflict of interest in mind, as employees of the ingredient supplier (Taiyo Kagaku) were among the authors.
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This randomized, placebo-controlled, crossover, and double-blind trial aimed to examine the possible effects of four weeks L-theanine administration on stress-related symptoms and cognitive functions in healthy adults. Participants were 30 individuals (nine men and 21 women; age: 48.3 ± 11.9 years) who had no major psychiatric illness. L-theanine (200 mg/day) or placebo tablets were randomly and blindly assigned for four-week administration. For stress-related symptoms, Self-rating Depression Scale, State-Trait Anxiety Inventory-trait, and Pittsburgh Sleep Quality Index (PSQI) scores decreased after L-theanine administration (p = 0.019, 0.006, and 0.013, respectively). The PSQI subscale scores for sleep latency, sleep disturbance, and use of sleep medication reduced after L-theanine administration, compared to the placebo administration (all p < 0.05). For cognitive functions, verbal fluency and executive function scores improved after L-theanine administration (p = 0.001 and 0.031, respectively). Stratified analyses revealed that scores for verbal fluency (p = 0.002), especially letter fluency (p = 0.002), increased after L-theanine administration, compared to the placebo administration, in individuals who were sub-grouped into the lower half by the median split based on the mean pretreatment scores. Our findings suggest that L-theanine has the potential to promote mental health in the general population with stress-related ailments and cognitive impairments. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.
View original ↗ PMID 39633316 The effects of L-theanine supplementation on the outcomes of patients with mental disorders: a systematic review Systematic review · BMC Psychiatry, 2024 11 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s (patients with mental disorders) - as an add-on, symptoms fell more than controls in schizophrenia, anxiety disorders, and ADHD. Mostly small medication-combined studies, so an independent effect is uncertain.
Key summary
A systematic review of L-theanine supplementation (mostly as a medication add-on) in patients with mental disorders (11 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s across six countries). It reported that psychiatric symptoms fell more in the L-theanine group than controls in schizophrenia, anxiety disorders, and ADHD. However, the conditions covered (schizophrenia, ADHD, OCD, depression, sleep disorders, generalized anxiety, Tourette) were varied and mostly small studies combined with medication, so the authors said further research is needed to validate the findings and clarify mechanisms. This is a narrative synthesis, not a meta-analysisA statistical synthesis combining results of multiple studies into one conclusion..
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BACKGROUND: When utilized as an adjunct with antidepressants, antipsychotics, and other psychopharmacological drugs, certain amino acids, such as L-Theanine (LT), have shown potential effectiveness in enhancing the symptomatic outcomes of patients with mental disorders. Despite this, there is a lack of previous systematic reviews examining these associations. Therefore, we conducted a systematic review of randomized controlled trials examining these relationships. METHODS: A comprehensive systematic review was conducted, scouring six electronic databases (PubMed, Scopus, PsycINFO, Web of Science, CINAHL Complete, and Cochrane) from their inception up to June 2023, specifically focusing on randomized controlled trials that investigated the effects of LT supplementation on the outcomes of patients with mental health disorders. The Cochrane Risk of Bias Tool for Randomized Trials was employed to assess the quality of the included studies. RESULTS: Among the 419 publications identified, 11 studies from six countries - Israel, Iran, the USA, Japan, Australia, and Italy - were included in the final analysis. These studies covered a range of mental disorders, including schizophrenia, Attention-Deficit/Hyperactivity Disorder (ADHD), Obsessive-Compulsive Disorder (OCD), Major Depressive Disorder (MDD), sleep disorders, Generalized Anxiety Disorder (GAD), and Tourette syndrome. The findings demonstrated that LT supplementation reduced psychiatric symptoms more effectively than control conditions in individuals with schizophrenia, anxiety disorders, and ADHD. CONCLUSIONS: 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. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.
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