L-Theanine Research
39 peer-reviewed studies · Evidence score: 9/10
The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis
Bulman A et al. • Sleep medicine reviews (2025)
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- 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.Copyright © 2025 The Author(s).
- Published by Elsevier Ltd..
Efficiency of Different Supplements in Alleviating Symptoms of ADHD with or Without the Use of Stimulants: A Systematic Review
Al Shahab S et al. • Nutrients (2025)
The evidence revealed the potential use of supplements as complementary ADHD treatments under clinical guidance.
- The evidence revealed the potential use of supplements as complementary ADHD treatments under clinical guidance.
- The limited effect of supplements cannot replace the well-documented efficacy of stimulants for ADHD treatment.
- Additional studies are needed to ascertain the most effective dosages and the safety of these supplements as adjunctive treatments for ADHD.
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
Payne ER et al. • Nutrition reviews (2025)
This meta-analysis provides evidence that theanine plus caffeine, and theanine alone, could be beneficial for cognitive and mood outcomes.
- 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.
- Further research warranted to confirm findings
The Role of Supplements and Over-the-Counter Products to Improve Sleep in Children: A Systematic Review
Innocenti A et al. • International journal of molecular sciences (2023)
Our focus was the utilization of over the counter (OTC) products, specifically iron, hydroxytryptophan, theanine and antihistamines in the management of different pediatric sleep disorders with the intention of providing a practical guide for the clinician.
- Although good sleep quality in children has been proven to be a key factor for optimal cognitive, physical and psychological development, a significant and ever-increasing percentage of the pediatric population suffers from sleep disorders.
- In children, behavioral interventions along with supplements are recommended as the first line treatment.
- This systematic review was conducted, according to the PRISMA guidelines, with the purpose of assessing the principal nutrients involved in the pathways of sleep-regulating neurotransmitters in children and adolescents.
Association between sleep pattern and pharmacological treatment in children with attention deficit disorder with hyperactivity: a systematic review
Rocha NS et al. • Revista paulista de pediatria : orgao oficial da Sociedade de Pediatria de Sao Paulo (2023)
The drugs used in the treatment of ADHD seem to have negative repercussions on the sleep quality of children, with the drug atomoxetine showing lesser effects on this variable.
- The drugs used in the treatment of ADHD seem to have negative repercussions on the sleep quality of children, with the drug atomoxetine showing lesser effects on this variable.
- Published in Revista paulista de pediatria : orgao oficial da Sociedade de Pediatria de Sao Paulo (2023)
- Further research warranted to confirm findings
Medicinal herbs for the treatment of anxiety: A systematic review and network meta-analysis
Zhang W et al. • Pharmacological research (2022)
Medicinal herbs may be promising for the treatment of anxiety.
- 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.
Theanine and cancer: A systematic review of the literature
Shojaei-Zarghani S et al. • Phytotherapy research : PTR (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.© 2021 John Wiley & Sons Ltd.
- 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.
The effects of L-theanine supplementation on the outcomes of patients with mental disorders: a systematic review
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.
- 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.
- Further research warranted to confirm findings
Green tea effects on cognition, mood and human brain function: A systematic review
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 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.
The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review
Williams JL et al. • Plant foods for human nutrition (Dordrecht, Netherlands) (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.
- 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.
To sleep or not to sleep: a systematic review of the literature of pharmacological treatments of insomnia in children and adolescents with attention-deficit/hyperactivity disorder
Barrett JR et al. • Journal of child and adolescent psychopharmacology (2013)
There is a relative paucity of evidence for the pharmacological treatment of ADHD-related sleep disorders; therefore, further research should be conducted to replicate these findings and obtain reliable results.
- There is a relative paucity of evidence for the pharmacological treatment of ADHD-related sleep disorders; therefore, further research should be conducted to replicate these findings and obtain reliable results.
- Published in Journal of child and adolescent psychopharmacology (2013)
- Further research warranted to confirm findings
Safety, Tolerability and Efficacy of Drugs for Treating Behavioural Insomnia in Children with Attention-Deficit/Hyperactivity Disorder: A Systematic Review with Methodological Quality Assessment
Anand S et al. • Paediatric drugs (2017)
There is generally poor evidence for prescribing drugs for behavioural insomnia in children with ADHD.
- There is generally poor evidence for prescribing drugs for behavioural insomnia in children with ADHD.
- Further controlled studies are warranted.
- Further research warranted to confirm findings
Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis
Camfield DA et al. • Nutrition reviews (2014)
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.© 2014 International Life Sciences Institute.
- 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.© 2014 International Life Sciences Institute.
- Standardized mean differences between placebo and treatment groups are presented for each study and outcome measure.
Perioperative Administration of Cystine and Theanine Suppresses Inflammation and Facilitates Early Rehabilitation and Recovery after Esophagectomy: A Randomized, Double-Blind, Controlled Clinical Trial
Okamoto H et al. • Nutrients (2022)
This study suggests that perioperative administration of CT may contribute to early recovery and rehabilitation after esophagectomy via suppression of inflammatory response.
- Although the CT group (n = 16) showed better patient activity across the investigated period, there was no significant difference between the two groups.
- However, white blood cell count on postoperative days (POD) 2 and 10, neutrophil count (POD 2, 7, and 10), and C-reactive protein level (POD 13) in the CT group were significantly lower than in the placebo group.
- Furthermore, 6MWT on POD 7 and QoR-40 on POD 13 were significantly higher in the CT group than those in the placebo group.
Effect of Alpha-S1-Casein Tryptic Hydrolysate and L-Theanine on Poor Sleep Quality: A Double Blind, Randomized Placebo-Controlled Crossover Trial
Thiagarajah K et al. • Nutrients (2022)
Further studies with a larger number participants are warranted to support these findings.
- 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.
l-theanine adjunct to sertraline for major depressive disorder: A randomized, double-blind, placebo-controlled clinical trial
Shamabadi A et al. • Journal of affective disorders (2023)
l-theanine adjunct to sertraline outperforms placebo in treating MDD in a safe manner.
- l-theanine adjunct to sertraline outperforms placebo in treating MDD in a safe manner.
- Further long-term, large-scale studies are recommended to confirm this evidence.
- Further research warranted to confirm findings
Nutritional Modulation of Sleep Latency, Duration, and Efficiency: A Randomized, Repeated-Measures, Double-Blind Deception Study
Langan-Evans C et al. • Medicine and science in sports and exercise (2023)
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.
- 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.
Analysis of the Effects of Known Sleep-Support Supplements in Relation to Life Habits, Sleep Conditions, and Sleep Problems
Imafuku F et al. • Nutrients (2023)
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.
- 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.
Effect of single or combined caffeine and L-Theanine supplementation on shooting and cognitive performance in elite curling athletes: a double-blind, placebo-controlled study
Yilmaz U et al. • Journal of the International Society of Sports Nutrition (2023)
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.
- 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.
L-theanine combination therapy with fluvoxamine in moderate-to-severe obsessive-compulsive disorder: A placebo-controlled, double-blind, randomized trial
Nematizadeh M et al. • Psychiatry and clinical neurosciences (2023)
Findings in this study suggest L-theanine as a relatively safe and effective adjuvant therapy for moderate to severe OCD.
- Findings in this study suggest L-theanine as a relatively safe and effective adjuvant therapy for moderate to severe OCD.
- Published in Psychiatry and clinical neurosciences (2023)
- Further research warranted to confirm findings