The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review


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.

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Preferred Reporting Items for Systematic Reviews and Meta-Analyses


Randomised Controlled Trial


Hypothalamic Pituitary Adrenal


Heart Rate


Heart Rate Variability


Profile of Mood States


Visual Analog Scale


State-Trait Anxiety Inventory


Beck’s Anxiety Inventory


Mood, Alertness and Physical Symptoms Questionnaire


Depression Anxiety and Stress Scale


Visual Probe Task


Visual Analogue Mood Scale


Hamilton Anxiety Rating Scale


salivary Alpha-Amylase (sAA)


Salivary Immunoglobulin A


Blood Pressure


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Dr. Paul Roach for providing initial feedback on the manuscript.


J Williams is supported by an Australian Government Research Training Program scholarship. N.M. D’Cunha is supported by a Dementia Australia Research Foundation PhD scholarship. All other authors declare no funding sources.

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Correspondence to Nenad Naumovski.

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Williams, J.L., Everett, J.M., D’Cunha, N.M. et al. The 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 75, 12–23 (2020).

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  • L-theanine
  • Stress response
  • Anxiety
  • Mental health
  • Green tea
  • Human trials