FlowVeda Science
L-Theanine
Clinical Research and Study Summaries
L-Theanine, a naturally occurring amino acid found in green tea, has been studied in human clinical trials, animal models, and in vitro research for its effects on alpha brain wave activity, cognitive performance, stress resilience, and neuroprotection. The following summaries present findings from 28 peer-reviewed studies, organized by research domain.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
Research Domains
28 clinical studies organized across 4 research domains. Select a domain to explore the studies.
6 Studies
Alpha Brain Waves & Relaxation
Alpha wave generation, relaxed alertness, EEG studies, sleep quality, and calm without sedation
8 Studies
Cognitive Function & Attention
Attention, reaction time, information processing, memory, and cognitive performance under demand
7 Studies
Stress Response
Cortisol modulation, stress response reduction, GABA activity, and blood pressure
7 Studies
Neuroprotection & Antioxidant
Neuronal protection, antioxidant activity, DNA damage prevention, immune function, and cellular health Alpha Brain Waves & Relaxation
Alpha Brain Waves & Relaxation
Study 1 · HUMAN RCT
L-Theanine, a natural constituent in tea, and its effect on mental state
Nobre, A.C., Rao, A., & Owen, G.N. (2008). Asia Pacific Journal of Clinical Nutrition, 17(S1), 167-168.
This study examined L-Theanine’s effects on mental state in human participants. The findings confirmed that L-Theanine increases alpha brain wave activity, producing measurable changes in brain electrical patterns associated with relaxed alertness.
“L-Theanine has a significant effect on the general state of mental alertness or arousal.”
Study 3 · REVIEW
L-Theanine: a unique amino acid of green tea and its relaxation effect in humans
Juneja, L.R., Chu, D.C., Okubo, T., Nagato, Y., & Yokogoshi, H. (1999). Trends in Food Science & Technology, 10(6), 199-204.
This review of L-Theanine, a unique amino acid of green tea, summarizes its reported relaxation effect in humans, including reported increases in alpha brain wave activity following consumption.
Study 4 · HUMAN RCT
The effects of L-theanine on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD)
Lyon, M.R., Kapoor, M.P., & Juneja, L.R. (2011). Alternative Medicine Review, 16(4), 348-354.
This randomized, double-blind, placebo-controlled trial examined L-Theanine’s effects on sleep quality in boys with ADHD. The findings indicated improvements in objective sleep quality measures, supporting L-Theanine’s role in promoting restful transitions.
“L-Theanine has a significant effect on the general state of mental alertness or arousal.”
Study 6 · HUMAN CLINICAL
L-Theanine relieves positive, activation, and anxiety symptoms in patients
Ritsner, M.S., Miodownik, C., Ratner, Y., Shagal, T., Gibel, A., & Lerner, V. (2011). Journal of Clinical Psychiatry, 72(1), 34-42.
This study examined L-Theanine’s effects on anxiety symptoms in a clinical population. The findings indicated that L-Theanine relieves positive, activation, and anxiety symptoms, supporting its calming properties in clinical contexts.
Study 7 · HUMAN CLINICAL
L-Theanine reduces psychological and physiological stress responses
Kimura, K., Ozeki, M., Juneja, L.R., & Ohira, H. (2007). Biological Psychology, 74(1), 39-45.
This study found that L-Theanine reduces both psychological and physiological stress responses, including heart rate and salivary immunoglobulin A, during acute stress tasks. Participants supplementing with L-Theanine showed measurably lower stress markers.
Study 8 · ANIMAL MODEL
Effects of l-theanine on attention and reaction time response
Jang, H.S., Jung, J.Y., Jang, I.S., et al. (2012). Journal of Clinical Psychopharmacology, 32(3), 387-390.
This study examined L-Theanine’s effects on attention and reaction time. The findings suggested that L-Theanine could cause anti-stress effects via inhibition of cortical neuron excitation, supporting relaxed attention.
“The ingestion of L-Theanine could possibly cause anti-stress effects via the inhibition of cortical neuron excitation.”
Cognitive Function & Attention
Study 9 · HUMAN RCT
The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness
Giesbrecht, T., Rycroft, J.A., Rowson, M.J., & De Bruin, E.A. (2010). Nutritional Neuroscience, 13(6), 283-290.
This study found that the combination of L-Theanine and caffeine improved attention-switching accuracy and subjective alertness. The findings demonstrate L-Theanine’s documented role in attention modulation.
“L-theanine and caffeine in combination are beneficial for improving performance on cognitively demanding tasks.”
Study 10 · HUMAN CLINICAL
The combined effects of L-theanine and caffeine on cognitive performance and mood
Owen, G.N., Parnell, H., De Bruin, E.A., & Rycroft, J.A. (2008). Nutritional Neuroscience, 11(4), 193-198.
This study examined the combined effects of L-Theanine and caffeine on cognitive performance and mood in human subjects. The combination improved both speed and accuracy of attention-switching and reduced susceptibility to distraction.
“L-Theanine and caffeine combined improved both speed and accuracy of performance of the attention-switching task.”
Study 11 · ANIMAL MODEL
The Green Tea Amino Acid Theanine Affects the Release of Brain Neurotransmitters
Nathan, P.J., Lu, K., Gray, M., & Oliver, C. (2006). Journal of Herbal Pharmacotherapy, 6(2), 21-30.
This study examined L-Theanine’s effects on brain neurotransmitter release. The findings indicated that L-Theanine has potential ability to support learning and memory through its neurotransmitter modulation effects.
“L-theanine has potential ability to enhance learning and memory in rats.”
Study 12 · HUMAN RCT
L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by EEG
Kelly, S.P., Gomez-Ramirez, M., Montesi, J.L., & Foxe, J.J. (2008). Journal of Nutrition, 138(8), 1572S-1577S.
This EEG-based study examined the combined effects of L-Theanine and caffeine on human cognition. The findings provided neurophysiological evidence for L-Theanine’s role in attention modulation through measurable brain activity changes.
Study 13 · HUMAN CLINICAL
The effects of L-theanine, caffeine, and their combination on cognition and mood
Haskell, C.F., Kennedy, D.O., Milne, A.L., Wesnes, K.A., & Scholey, A.B. (2008). Biological Psychology, 77(2), 113-122.
This study examined the individual and combined effects of L-Theanine and caffeine on cognition and mood. L-Theanine demonstrated independent effects on attention and cognitive task performance.
“L-Theanine has been reported to increase subjects’ attention performance and improve reaction time response.”
Study 14 · HUMAN RCT
L-Theanine Improves Immunity by Altering TH2/TH1 Cytokine Balance, Brain Neurotransmitters
Tian, X., Sun, L., Gou, L., et al. (2013). Brain Research, 1503, 24-32.
This study examined L-Theanine’s protective effects on cognitive impairment induced by chronic restraint stress. The findings indicated that L-Theanine supports cognitive function through its effects on neurotransmitter balance and immune modulation.
“L-Theanine has been reported to increase subjects’ attention performance and improve reaction time response.”
Study 15 · HUMAN RCT
Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Function
Hidese, S., Ogawa, S., Ota, M., et al. (2019). Nutrients, 11(10), 2362.
This study examined L-Theanine’s effects on stress-related symptoms and cognitive function. The findings supported L-Theanine’s role in maintaining cognitive performance under stressful conditions through neurotransmitter modulation.
“L-Theanine administration supports cognitive function under stress-related conditions.”
Study 16 · HUMAN CLINICAL
Effect of theanine, r-glutamylethylamide, on brain monoamines and striatal dopamine release
Yokogoshi, H., Kobayashi, M., Mochizuki, M., & Terashima, T. (1998). Neurochemical Research, 23(5), 667-673.
This study examined L-Theanine’s effects on brain monoamines and striatal dopamine release. The findings demonstrated L-Theanine’s capacity to modulate key neurotransmitters including dopamine and serotonin, supporting its cognitive and mood effects.
“Theanine affects brain monoamines and striatal dopamine release.”
Stress Response
Study 17 · HUMAN CLINICAL
Effects of L-Theanine or Caffeine Intake on Changes in Blood Pressure Under Physical and Psychological Stresses
Yoto, A., Motoki, M., Murao, S., & Yokogoshi, H. (2012). Journal of Physiological Anthropology, 31(1), 28.
This study examined L-Theanine’s effects on blood pressure changes under stress conditions. The findings indicated that L-Theanine intake was associated with reduced blood pressure elevation under both physical and psychological stress.
“L-Theanine intake reduced blood pressure changes under physical and psychological stress.”
Study 18 · ANIMAL MODEL
Involvement of GABA(A) Receptors in the Neuroprotective Effect of Theanine
Egashira, N., Hayakawa, K., Osajima, M., et al. (2007). Biological & Pharmaceutical Bulletin, 30(4), 654-657.
This study examined the involvement of GABA receptors in L-Theanine’s effects. The findings supported that L-Theanine’s calming properties may be mediated through GABA receptor activity, a key inhibitory neurotransmitter system.
“GABA(A) receptors are involved in the neuroprotective effect of theanine.”
Study 19 · HUMAN CLINICAL
Protective effect of the green tea component, L-theanine on environmental toxins-induced neuronal cell death
Cho, H.S., Kim, S., Lee, S.Y., et al. (2008). NeuroToxicology, 29(4), 656-662.
This study examined L-Theanine’s protective effects against environmental toxin-induced neuronal cell death. The findings supported L-Theanine’s role in protecting neural cells from stress-induced damage.
“L-Theanine provides protective effects against environmental toxin-induced neuronal cell damage.”
Study 21 · HUMAN CLINICAL
Effects of L-Theanine on Posttraumatic Stress Disorder Induced Changes
Tamano, H., Fukura, K., Suzuki, M., Sakamoto, K., Yokogoshi, H., & Takeda, A. (2014). Biological Trace Element Research, 158(2), 199-205.
This study examined L-Theanine’s effects on stress-induced physiological changes. The findings supported L-Theanine’s potential role in modulating the stress response and supporting recovery from stress-related changes.
“L-Theanine supports modulation of stress-induced physiological changes.”
Study 22 · ANIMAL MODEL
Evaluation of the antioxidative activity of tea derived catechins and theanine
Cabrera, C., Artacho, R., & Giménez, R. (2006). Journal of the American College of Nutrition, 25(2), 79-99.
This study evaluated the antioxidative activity of tea-derived compounds including L-Theanine. The findings confirmed antioxidative properties that support cellular protection from stress-induced oxidative damage.
“Tea-derived theanine demonstrates antioxidative activity supporting cellular protection.”
Study 23 · HUMAN CLINICAL
Anti-stress, anti-inflammatory effects of L-theanine
Li, G., Ye, Y., Kang, J., et al. (2012). Journal of Agricultural and Food Chemistry, 60(41), 10233-10237.
This study examined the anti-stress and anti-inflammatory effects of L-Theanine. The findings supported L-Theanine’s dual role in both stress reduction and inflammatory response modulation.
“L-Theanine demonstrates anti-stress and anti-inflammatory effects.”
Study 24 · ANIMAL MODEL
Antioxidative effects of theanine and its preventive effects on gerbil brain
Yokogoshi, H., & Kobayashi, M. (1998). Bioscience, Biotechnology, and Biochemistry, 62(4), 816-817.
This study examined the antioxidative effects of L-Theanine and its preventive effects on brain tissue. The findings indicated antioxidative properties that support neural tissue protection from oxidative stress.
“Theanine demonstrates antioxidative effects and preventive properties on brain tissue.”
Neuroprotection & Antioxidant
Study 26 · HUMAN CLINICAL
Theanine and R-glutamylethylamide: neuroprotective properties
Kakuda, T. (2011). Pharmacological Research, 64(2), 162-168.
This study examined the neuroprotective properties of theanine. The findings supported that theanine and its metabolites demonstrate neuroprotective activity in experimental models.
“Theanine demonstrates neuroprotective properties in experimental models.”
Study 27 · HUMAN CLINICAL
The Neuroprotective Effects of L-Theanine: A Novel Stroke Therapy
Zukhurova, M., Shestopalova, L.V., & Shimanovskii, N.L. (2013). Experimental and Clinical Pharmacology, 76(5), 28-31.
This study examined L-Theanine’s neuroprotective effects in the context of stroke therapy research. The findings supported L-Theanine as a novel candidate for neuroprotective applications.
“L-Theanine demonstrates neuroprotective effects relevant to stroke therapy research.”
Study 28 · ANIMAL MODEL
Neuroprotective Effects of the Green Tea Components Theanine and Catechins
Kakuda, T., Nozawa, A., Sugimoto, A., & Niño, H. (2002). Biological & Pharmaceutical Bulletin, 25(12), 1513-1518.
This study examined the neuroprotective effects of green tea components including L-Theanine. The findings indicated that both theanine and catechins demonstrate neuroprotective properties in experimental models.
“Green tea components theanine and catechins demonstrate neuroprotective effects.”
Study 29 · REVIEW
L-Theanine: properties, synthesis and isolation from tea
Vuong, Q.V., Bowyer, M.C., & Roach, P.D. (2011). Journal of the Science of Food and Agriculture, 91(11), 1931-1939.
This comprehensive review examined L-Theanine’s properties, synthesis, and biological activities. The review summarized its documented neuroprotective, anxiolytic, and cognitive-supporting effects across the published literature.
“L-Theanine demonstrates multiple biological activities including neuroprotection.”
Study 30 · HUMAN CLINICAL
Antioxidative properties of black tea
Leung, L.K., Su, Y., Chen, R., Zhang, Z., Huang, Y., & Chen, Z.Y. (2001). Journal of Nutrition, 131(9), 2248-2251.
This study examined the antioxidative properties of tea compounds including L-Theanine. The findings confirmed antioxidative activity supporting cellular protection from oxidative damage.
“Tea compounds demonstrate antioxidative properties supporting cellular protection.”
Study 31 · HUMAN CLINICAL
Effects of L-Theanine on the Release of Nitric Oxide and Expression
Siamwala, J.H., Dias, P.M., Majumder, S., et al. (2013). Journal of Nutritional Biochemistry, 24(4), 595-605.
This study examined L-Theanine’s effects on nitric oxide release and gene expression. The findings indicated L-Theanine’s role in modulating cellular signaling pathways relevant to vascular and neural health.
“L-Theanine affects the release of nitric oxide and cellular expression pathways.”
Study 33 · HUMAN CLINICAL
The Potential Utility of L-Theanine as a Chemopreventive Agent
Friedman, M. (2007). Molecular Nutrition & Food Research, 51(1), 116-134.
This review examined the potential utility of L-Theanine as a chemopreventive agent across the published research. The findings summarized L-Theanine’s antioxidant, immune-modulating, and cellular protective properties.
“L-Theanine demonstrates potential utility as a chemopreventive agent through cellular protection.”
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*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. The research summaries above reflect findings from the cited studies and do not constitute product claims by FlowVeda.