Theanine

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    Bill Willis, Thomas Solomon

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    Nick Milazzo, Katie Jantz
    Last Updated: September 4, 2025

    Theanine, also commonly referred to as L-theanine, is a naturally occurring amino acid found in tea. Supplementation with L-theanine may help reduce stress and anxiety and might improve sleep quality and some aspects of cognitive function.

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    Overview

    Dosage information

    Clinical studies typically use L-theanine at a dosage of 100–400 milligrams (mg) per day.

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    Examine Database References

    1. Reaction Time - Akiko Higashiyama, Hla Hla Htay, Makoto Ozeki, Lekh R. Juneja, Mahendra P. KapoorEffects of l-theanine on attention and reaction time responseJournal of Functional Foods.()
    2. Reaction Time - Chanaka N Kahathuduwa, Tharaka L Dassanayake, A M Tissa Amarakoon, Vajira S WeerasingheAcute effects of theanine, caffeine and theanine-caffeine combination on attentionNutr Neurosci.(2017 Jul)
    3. Reaction Time - Crystal F Haskell, David O Kennedy, Anthea L Milne, Keith A Wesnes, Andrew B ScholeyThe effects of L-theanine, caffeine and their combination on cognition and moodBiol Psychol.(2008 Feb)
    4. Reaction Time - Chanaka N Kahathuduwa, Chathurika S Dhanasekara, Shao-Hua Chin, Tyler Davis, Vajira S Weerasinghe, Tharaka L Dassanayake, Martin Binksl-Theanine and caffeine improve target-specific attention to visual stimuli by decreasing mind wandering: a human functional magnetic resonance imaging studyNutr Res.(2018 Jan)
    5. Reaction Time - John J Foxe, Kristen P Morie, Peter J Laud, Matthew J Rowson, Eveline A de Bruin, Simon P KellyAssessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention taskNeuropharmacology.(2012 Jun)
    6. Reaction Time - Peter J Rogers, Jessica E Smith, Susan V Heatherley, C W Pleydell-PearceTime for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and togetherPsychopharmacology (Berl).(2008 Jan)
    7. Executive Function - Shinsuke Hidese, Shintaro Ogawa, Miho Ota, Ikki Ishida, Zenta Yasukawa, Makoto Ozeki, Hiroshi KunugiEffects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled TrialNutrients.(2019 Oct 3)
    8. Executive Function - Grace E Giles, Caroline R Mahoney, Tad T Brunyé, Holly A Taylor, Robin B KanarekCaffeine and theanine exert opposite effects on attention under emotional arousalCan J Physiol Pharmacol.(2017 Jan)
    9. Executive Function - Yoshitake Baba, Shun Inagaki, Sae Nakagawa, Toshiyuki Kaneko, Makoto Kobayashi, Takanobu TakiharaEffects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled StudyJ Med Food.(2021 Apr)
    10. Attention - Simon P Kelly, Manuel Gomez-Ramirez, Jennifer L Montesi, John J FoxeL-theanine and caffeine in combination affect human cognition as evidenced by oscillatory alpha-band activity and attention task performanceJ Nutr.(2008 Aug)
    11. Attention - F L Dodd, D O Kennedy, L M Riby, C F Haskell-RamsayA double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and moodPsychopharmacology (Berl).(2015 Jul)
    12. Attention - Dassanayake TL, Kahathuduwa CN, Weerasinghe VSL-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover study.Nutr Neurosci.(2022-Apr)
    13. Prepulse Inhibition - Miho Ota, Chisato Wakabayashi, Junko Matsuo, Yukiko Kinoshita, Hiroaki Hori, Kotaro Hattori, Daimei Sasayama, Toshiya Teraishi, Satoko Obu, Hayato Ozawa, Hiroshi KunugiEffect of L-theanine on sensorimotor gating in healthy human subjectsPsychiatry Clin Neurosci.(2014 May)
    14. Attention - Shinsuke Hidese, Miho Ota, Chisato Wakabayashi, Takamasa Noda, Hayato Ozawa, Tsutomu Okubo, Hiroshi KunugiEffects of chronic l-theanine administration in patients with major depressive disorder: an open-label studyActa Neuropsychiatr.(2017 Apr)
    15. Anxiety Symptoms - Kimura K, Ozeki M, Juneja LR, Ohira HL-Theanine reduces psychological and physiological stress responsesBiol Psychol.(2007 Jan)
    16. Anxiety Symptoms - Williams JL, Everett JM, D'Cunha NM, Sergi D, Georgousopoulou EN, Keegan RJ, McKune AJ, Mellor DD, Anstice N, Naumovski NThe Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review.Plant Foods Hum Nutr.(2020-Mar)
    17. Salivary Alpha-Amylase - Keiko Unno, Naoki Tanida, Naoto Ishii, Hiroyuki Yamamoto, Kazuaki Iguchi, Minoru Hoshino, Atsushi Takeda, Hayato Ozawa, Tsutomu Ohkubo, Lekh Raj Juneja, Hiroshi YamadaAnti-stress effect of theanine on students during pharmacy practice: positive correlation among salivary α-amylase activity, trait anxiety and subjective stressPharmacol Biochem Behav.(2013 Oct)
    18. Stress Signs and Symptoms - Moulin M, Crowley DC, Xiong L, Guthrie N, Lewis EDSafety and Efficacy of AlphaWave(®) L-Theanine Supplementation for 28 Days in Healthy Adults with Moderate Stress: A Randomized, Double-Blind, Placebo-Controlled Trial.Neurol Ther.(2024 Aug)
    19. Sleep Quality - Bulman A, D'Cunha NM, Marx W, Turner M, McKune A, Naumovski NThe effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis.Sleep Med Rev.(2025 Feb 25)
    20. Sleep Quality - Lyon MR, Kapoor MP, Juneja LRThe effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trialAltern Med Rev.(2011 Dec)
    21. Sleep Quality - .(2024-06-16)
    22. Subjective Well-Being - Ai Yoto, Mao Motoki, Sato Murao, Hidehiko YokogoshiEffects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stressesJ Physiol Anthropol.(2012 Oct 29)
    23. Interleukin 4 - A Juszkiewicz, A Glapa, P Basta, E Petriczko, K Żołnowski, B Machaliński, J Trzeciak, K Łuczkowska, A Skarpańska-StejnbornThe effect of L-theanine supplementation on the immune system of athletes exposed to strenuous physical exerciseJ Int Soc Sports Nutr.(2019 Feb 15)
    24. Heart Rate - Jackson Williams, Andrew J McKune, Ekavi N Georgousopoulou, Jane Kellett, Nathan M D'Cunha, Domenico Sergi, Duane Mellor, Nenad NaumovskiThe Effect of L-Theanine Incorporated in a Functional Food Product (Mango Sorbet) on Physiological Responses in Healthy Males: A Pilot Randomised Controlled TrialFoods.(2020 Mar 23)
    25. Anxiety Symptoms - Kristy Lu, Marcus A. Gray, Chris Oliver, David T. Liley, Ben J. Harrison, Cali F. Bartholomeusz, K. Luan Phan and Pradeep J. NathanThe acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humansHuman Psychopharmacology.()
    26. Insomnia Signs and Symptoms - Sarris J, Byrne GJ, Cribb L, Oliver G, Murphy J, Macdonald P, Nazareth S, Karamacoska D, Galea S, Short A, Ee C, Birling Y, Menon R, Ng CHL-theanine in the adjunctive treatment of generalized anxiety disorder: A double-blind, randomised, placebo-controlled trialJ Psychiatr Res.(2019 Mar)
    27. Cortisol - Chanoch Miodownik, Rachel Maayan, Yael Ratner, Vladimir Lerner, Leonid Pintov, Maria Mar, Abraham Weizman, Michael S RitsnerSerum levels of brain-derived neurotrophic factor and cortisol to sulfate of dehydroepiandrosterone molar ratio associated with clinical response to L-theanine as augmentation of antipsychotic therapy in schizophrenia and schizoaffective disorder patientsClin Neuropharmacol.(Jul-Aug 2011)
    28. Subjective Well-Being - Ritsner MS, Miodownik C, Ratner Y, Shleifer T, Mar M, Pintov L, Lerner VL-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder: an 8-week, randomized, double-blind, placebo-controlled, 2-center studyJ Clin Psychiatry.(2011 Jan)