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Theanine – Simple, Safe, My Favorite Uses By Dr Tori Hudson, ND

Theanine Simple Safe My Favorite Uses

Theanine is a nonprotein amino acid that was first isolated from green tea and is chemically similar in structure to glutamic acid. L-theanine is the predominant isomer and is the subject of most of the research. One of the appealing aspects of using L-theanine is it’s safety profile and it’s only drug interaction listed is with antihypertensives in that there might be an augmented effect in lowering blood pressure, which is desirable to me in that perhaps my patient could end up needing a lower dose of the antihypertensive.

Even in children 8-12 years old, L-theanine has been used at doses of 200 mg bid for up to 6 weeks. In adults, up to 900 mg has been used daily for eight weeks. I have not used more than 200 mg tid, and granted, I have used it longer than eight weeks. But I am comfortable using it long term if folks gain benefit and need it.

Most of my experience with using L-theanine is in general anxiety disorders, co-existing depression-anxiety, stress, and to a lesser degree, cognitive function. I will focus on those.  

Oral L-theanine may improve some aspects of cognitive function and it might even work better when using it with caffeine. A single dose of 100 mg seems to improve attention and reduce errors in cognitive function tests.1 On the other hand, taking L-theanine at 200 mg/day for one month did not improve verbal fluency, memory, motor speed of executive function in adults although it may improve verbal fluency in adults with lower cognitive function testing.2

I mentioned using it with caffeine, and in a meta-analysis and multiple individual clinical studies the combination of L-theanine and caffeine appears to improve alertness and accuracy while not improving reaction time.3,4,5,6 While some research shows that L-theanine plus caffeine improves cognitive performance and lessens task-induced fatigue, it is not clear if this is due to just one of the ingredients or the combination.3,5,6 If you are thinking about Alzheimer’s disease prevention or intervention, there is insufficient evidence to support this use at this time.

One of my mainstay nutraceuticals for general anxiety disorder is L-theanine, despite the conflicting clinical research. One randomized, placebo-controlled, crossover and double-blind trial evaluated the effects of 200 mg/day L-theanine vs placebo for four weeks in nine men and 21 women on stress-related symptoms and cognitive functions.7 The Self-rating Depression Scale, State-Trait Anxiety Inventory-trait, and Pittsburgh Sleep Quality Index (PSQI) scores decreased after L-theanine administration. The PSQI subscale scores for sleep latency, sleep disturbance, and use of sleep medication reduced after L-theanine administration as well. In addition, cognitive functions, verbal fluency and executive function scores improved after L-theanine administration. Research reported that the findings suggest that L-theanine has the potential to promote mental health in the general population with stress-related ailments and cognitive impairments.

However, another small clinical study showed that taking a single dose of 200 mg of L-theanine does not reduce experimentally induced anticipatory anxiety when compared with placebo.8

It’s not clear if L-theanine improves depression but as we know, depression andanxiety often co-exist. There was a small clinical study demonstrating that taking 250 mg/day of a specific L-theanine product at bedtime for 8 weeks reduces mild depression and improves sleep quality compared to baseline.9 However, there was not a placebo or comparison group. 

For an anticipated stressful event, one might think of L-theanine just prior. One very small clinical study shows that 200 mg prior to a stress-inducing exam reduces tension/anxiety when compared with placebo.10 Other clinical research implies that taking 200 mg twice daily for one week prior to and the first 10 days of a stressful period decreases subjective stress scores when compared with placebo.11 While it seems to be able to induce a feeling of calm, it may not consistently be effective for anticipatory anxiety.12

I have not found any clear information about overdose issues and studies have not exceeded eight weeks. To my knowledge, I have not seen any consequences of overdosing, but my comfort zone has been a maximum of 200 mg three times daily for ongoing use. I do think another use of it is as-needed, or short-term use for anticipated or immediate stressful times. Another aspect that I like about using L-theanine is I can easily use it daily along with other products such as lavender extract for general anxiety. 


  1. Foxe JJ, et al. Assessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention task. Neuropharmacology. 2012;62(7):2320-2327. 
  2. Hidese S, Ogawa S, Ota M, et al. Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: A randomized controlled trial. Nutrients. 2019;11(10). pii: E2362. 
  3. Giesbrecht, T., Rycroft, J. A., Rowson, M. J., and De Bruin, E. A. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci. 2010;13(6):283-290. 
  4. Camfield DA, Stough C, Farrimond J, Scholey AB. Actue effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis. Nutr Rev. 2014;72(8):507-522.
  5. Owen GN, Parnell H, De Bruin EA, Rycroft JA. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci 2008;11(4):193-8
  6. Einöther SJ, Martens VE, Rycroft JA, De Bruin EA. L-theanine and caffeine improve task switching but not intersensory attention or subjective alertness. Appetite 2010;54(2):406-9
  7. Hidese S, Ogawa S, Ota M, et al. Effects of L-theanine administration on stress-related symptoms and cognitive functions in healthy adults: A randomized controlled trial. Nutrients. 2019;11(10).
  8. Lu K, Gray MA, Oliver C, et al. The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans. Hum Psychopharmacol 2004;19:457-65. 
  9. Hidese S, Ota M, Wakabayashi C, et al. Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study. Acta Neuropsychiatr 2017;29(2):72-9. 
  10. Yoto A, Motoki M, Murao S, Yokogoshi H. Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses. J Physiol Anthropol. 2012;31:28. 
  11. Unno K, et al. Anti-stress effect of theanine on students during pharmacy practice: positive correlation among salivary a-amylase activity, trait anxiety and subjective stress. Pharmacol Biochem Behav. 2013;111:128-135. 
  12. Lu K, Gray MA, Oliver C, et al. The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans. Hum Psychopharmacol 2004;19:457-65.