Ever wondered why you were told to drink a cup of tea before bed to help you relax? Tea isn't just a good source of antioxidants—it also contains a unique amino acid, L-theanine, which has received recent attention for claimed “stress-reducing” effects. And though many "stress-reducing" supplements have come to market to combat the recent rise in societal stress, many don't live up to their claims. So what makes L-theanine different? Is L-theanine safe and effective to take to relieve stress? Here's a breakdown of the research.
Understanding the body's response to stress
Though everyone experiences stress differently, it’s typically defined as "the brain’s response to any new demand.” Acute stressors, for example, are immediate and intense, while chronic stress is more prolonged and sustained. Chronic stress can negatively impact mental and physical health—in the long term, chronic stress may contribute to a variety of health problems like heart disease, high blood pressure, diabetes, depression, and anxiety. Researchers have aimed to evaluate ways to manage stress in order to reduce the risk of negative health effects.
What is L-theanine and what are its effects?
Theanine is an amino acid found primarily in green and black tea and some mushrooms. It’s also available in pill or tablet form. This nutrient is best known for its potential to reduce stress and promote relaxation while simultaneously improving alertness.
L-theanine is thought to work by decreasing “excitatory” brain chemicals that contribute to stress and anxiety while increasing brain chemicals that promote the feeling of relaxation. These effects have been demonstrated continuously in animal studies which have found L-theanine to be associated with improvements in mood, cognition, and reduction of anxiety-like symptoms.[4,5,6] However, it is important to remember that findings in animal studies don't necessarily translate to humans. So let's dive into the recently available research unveiling the “stress-reducing” effect of L-theanine in humans.
L-theanine’s impact on stress and anxiety: Human studies
A recent 2016 systematic review looked at all available human clinical trials that examined the effects of supplemental L-theanine consumption (200-400 mg/day) on stress and anxiety. Of the five randomized controlled trials, four trials found that L-theanine was associated with reduced stress and anxiety in people experiencing stressful situations. However, these studies only looked at those experiencing acute stress, and more research is needed to evaluate L-theanine’s impact on chronic stress.
One randomized control trial showed particular promise for the future of L-theanine research. The study followed 30 healthy adults who were given either L-theanine (200 mg/day) or a placebo for four weeks. Stress-related symptoms and state-trait anxiety scores—anxiety about an event (state), or anxiety level as a personal characteristic (trait)—decreased significantly following L-theanine administration compared to the placebo. These findings demonstrate L-theanine’s potential to promote mental health in the general population facing stress-related ailments.
Longer-term and larger cohort clinical studies, including those in which L-theanine is incorporated as part of a regular diet, are needed to justify its clinical use as a therapeutic agent to reduce stress and anxiety in people exposed to stressful environments.
Are there other benefits of L-theanine supplementation?
L-theanine may be beneficial for those who experience increased blood pressure in stressful situations
One study found that L-theanine can help attenuate an increase in blood pressure for people who usually experienced higher blood pressure after specific mental tasks. But more research is needed to determine L-theanine’s effects on blood pressure. For now, read this article for science-backed tips on how to naturally prevent and lower blood pressure.
L-theanine may improve sleep quality
Unlike many sleep inducers, L-theanine is not a sedative—but it may help to improve sleep quality via relaxation. L-theanine's "relaxation" effects are primarily explained by its ability to decrease “excitatory” brain chemicals that contribute to stress and anxiety while also increasing brain chemicals that encourage a sense of calm.[10,11] One study found that doses of 250 mg and 400 mg of L-theanine greatly improved sleep in both animals and humans.  L-theanine also promotes relaxation without added drowsiness, making it useful any time of day.
L-theanine paired with caffeine may help increase focus and attention
One small study found that a combination of L-theanine (97 mg) and caffeine (40 mg) helped a group of young adults focus better during demanding tasks. A typical cup of coffee contains 95 mg of caffeine.
Another study compared the effects of 50 mg of caffeine, with and without 100 mg L-theanine, on cognition and mood in healthy participants. The L-theanine and caffeine combination improved both speed and accuracy of performance on attention-switching tasks, and reduced susceptibility to distractions when completing memory tasks compared to caffeine alone.  These results confirmed previous evidence suggesting that L-theanine and caffeine in combination are beneficial for improving performance on cognitively demanding tasks. [12,13]
Due to the small sample sizes and short duration of these studies, more research is needed to confirm L-theanine’s effect on cognitive performance. In the meantime, learn more about these science-proven habits that boost cognition.
Who should take L-theanine supplements?
Studies have primarily examined the impact of L-theanine on stress reduction, relaxation, and cognition in healthy adults. While these studies do show promising results for the use of L-theanine as a stress-reducer relaxation aid, more studies with larger sample sizes are needed to effectively make generalized recommendations. As always, be sure to speak with your physician before trying any nutritional supplements.
Are L-theanine supplements safe?
Studies have shown no direct side effects of taking L-theanine supplements, suggesting that it is safe to drink teas and take supplements that contain L-theanine. However, it’s important to remember that the Food and Drug Administration doesn’t regulate supplements. Manufacturers of those products bear the weight of the responsibility to make sure their products are safe.
How much L-theanine should you take?
Though more research is needed to conclude L-theanine’s effect on stress, a dose between 200-400 mg is recommended to use safely based on the available human studies.[1,2] When used in combination with 40-50mg of caffeine, around 100 mg of L-theanine has shown to be the most beneficial.[10,12,13]
InsideTracker currently recommends L-theanine supplements as part of the "Reduce Stress" goal. L-theanine is most helpful when taken for a short period of time surrounding a stressful event, rather than on a long-term basis.
Many biomarkers are impacted by stress, particularly cortisol AKA “the stress hormone.” InsideTracker analyzes cortisol and other biomarkers that are also associated with stress to help deliver personalized recommendations on how to reduce stress in your daily life. Purchase any InsideTracker blood plan, download the InsideTracker app, and make "Reduce Stress" your next InsideTracker goal.
If you’re looking to try L-theanine as a de-stressor:
- Add it to your InsideTracker action plan
- Set a text or email supplement reminder via your InsideTracker dashboard
Marianna Moore, MS, CSCSMarianna has her Masters of Science in Nutrition and as a certified strength and conditioning specialist with a BS in Exercise Science, she has a passion for helping others lead a healthier lifestyle. Marianna can be found in the kitchen creating new recipes or engaging in a new form of exercise. Follow her on Instagram @mariannas_pantry.
- Everett, J. M., Gunathilake, D., Dufficy, L., Roach, P. D., THOMAS, J., UPTON, D., & NAUMOVSKI, N. (2015). Theanine consumption, stress and anxiety in human clinical trials: a systematic review. 41-42. Abstract from 39th Annual Scientific Meeting of the Nutrition Society of Australia 2015, Wellington, New Zealand. https://doi.org/10.1016/j.jnim.2015.12.308
- U.S. Department of Health and Human Services. (n.d.). 5 things you should know about stress. National Institute of Mental Health. Retrieved October 25, 2021, from https://www.nimh.nih.gov/health/publications/stress.
- Vuong QV, Bowyer MC, Roach PD. L-theanine: properties, synthesis and isolation from tea. J Sci Food Agric. 2011;91(11):1931-9.
- Nathan PJ, Lu K, Gray M, et al. The neuropharmacology of L-theanine(N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent. J Herb Pharmacother. 2006;6(2):21-30.
- Tian X, Sun L, Gou L, et al. Protective effect of L-theanine on chronic restraint stress-induced cognitive impairments in mice. Brain Res. 2013;1503:24-32.
- Lardner AL. Neurobiological effects of the green tea constituent theanine and its potential role in the treatment of psychiatric and neurodegenerative disorders. Nutr Neurosci. 2014 Jul;17(4):145-55. doi: 10.1179/1476830513Y.0000000079. Epub 2013 Nov 26. PMID: 23883567.
- Hidese, S., Ogawa, S., Ota, M., Ishida, I., Yasukawa, Z., Ozeki, M., & Kunugi, H. (2019). Effects of L-theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients, 11(10), 2362. https://doi.org/10.3390/nu11102362
- Yoto, A., Motoki, M., Murao, S., & Yokogoshi, H. (2012). Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses. Journal of physiological anthropology, 31(1), 28. https://doi.org/10.1186/1880-6805-31-28
- Duygu Türközü & Nevin Şanlier (2017) L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety, Critical Reviews in Food Science and Nutrition, 57:8, 1681-1687, DOI: 10.1080/10408398.2015.101614.
- Rao TP, Ozeki M, Juneja LR. In Search of a Safe Natural Sleep Aid. J Am Coll Nutr. 2015;34(5):436-47. doi: 10.1080/07315724.2014.926153. Epub 2015 Mar 11. PMID: 25759004.
- Williams, J., KELLETT, J., Roach, P., MCKUNE, A., MELLOR, D., THOMAS, J., & NAUMOVSKI, N. (2016). L-theanine as a Functional Food Additive: Its Role in Disease Prevention and Health Promotion. Beverages, 2(2), 1-16. https://doi.org/10.3390/beverages2020013
- Giesbrecht T, Rycroft JA, Rowson MJ, De Bruin EA. The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci. 2010 Dec;13(6):283-90. doi: 10.1179/147683010X12611460764840. PMID: 21040626.
- 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 Aug;11(4):193-8. doi: 10.1179/147683008X301513. PMID: 18681988.