What is L-theanine & What Does It Do? All the Supplement's Benefits

Feb 22, 2022 Sleep TipsStress 5 MIN

What is L-theanine & What Does It Do? All the Supplement's Benefits

Quick Health Scoop

  • L-theanine occurs naturally in plant sources such as tea leaves and some mushrooms
  • As an amino acid, L-theanine increases calming brain chemicals
  • L-theanine uses include enhancing calm and focus (in combination with caffeine), relaxation, and sleep
  • The popularity of L-theanine is due to its ability to relax you without causing drowsiness

If you’re a tea drinker, you might already be familiar with one of its primary ingredients known as L-theanine. Found naturally in green and black tea (but also present in some mushrooms), this ingredient might provide a variety of health benefits, including helping you relax and sleep better. But what is L-theanine? And what does L-theanine do?

Read on to learn more about L-theanine benefits.

What is L-Theanine?

L-theanine is gaining popularity these days, showing up more frequently in food and supplements. Exactly what is L-theanine? This non-protein amino acid naturally occurs in plant sources such as tea leaves and some mushrooms. [1] The ingredient is sometimes added to supplements as well to help support relaxation before bedtime.

What Does L-Theanine Do to the Body?

Technically known as L-g-glutamylethylamide, L-theanine is quickly absorbed in the small intestine, crossing the blood-brain barrier, and delivering protective effects to nerve cells. [2]  Researchers think L-theanine may increase relaxing neurochemicals in the body and reduce stimulating ones. [3] 

What does L-theanine do in the brain? Here’s how it works: L-theanine increases the brain’s production of serotonin and dopamine production, and GABA. [4] Serotonin and dopamine (known as “the happy hormones”) and GABA are all neurotransmitters and play a role in regulating mood, emotion, alertness, concentration, sleep, and other bodily functions. [5] GABA acts as an inhibitor by slowing or blocking certain nerve signals, which affects how people may experience fear, and stress. 

Learn More: What Does GABA Do?

So, while L-theanine increases relaxing brain chemicals, it also lowers those linked to stress and anxiety, by acting on alpha 1 and 2 brain wave activity, which helps to relax your mind and prepare you for sleep or, when combined with caffeine, also helps to reduce mental fatigue and support focus)

What is L-theanine good for? The appeal of L-theanine stems from its ability to relax the body and mind without sedating it.

What are the Benefits of Taking L-Theanine?

Although larger-scale studies are needed, small-scale studies found a variety of L-theanine health benefits, especially in relation to L-theanine and sleep and stress. For example, research shows that L-theanine:

  • May help reduce acute stress in people experiencing stressful situations [6] 
  • May calm the mind without causing drowsiness [7] 
  • May help support sleep when combined with melatonin [8,9] 
  • May help reduce mental fatigue and support focus when paired with caffeine [10] 

When Should I Take L-Theanine?

Sometimes you might need help being more alert or less stressed, while other times you might need help sleeping. Therefore, when you take L-theanine depends on what you’re taking it for. 

If you’re drinking caffeinated tea, the combination of both caffeine and L-theanine will help promote alertness and enhance focus, so drink this in the morning. As a supplement, Nature Made’s Clear & Focus combines L-theanine and green tea caffeine—a synergistic mix shown to help reduce mental fatigue, and support focus and attention—plus five B vitamins that help support healthy brain cell function (Read More: Types of Vitamin B). Take in the morning or as needed.

On the other hand, if you need help getting to sleep, you’ll want to skip the caffeine and drink decaffeinated or herbal tea at night. As one of our sleep supplements, Nature Made Sleep Longer™ combines melatonin, GABA, and L-Theanine, so take this at night to help calm your mind, fall asleep faster, and stay asleep longer. 

As mentioned earlier, L-theanine is often paired with other ingredients (such as caffeine or melatonin) to work in tandem. That’s why Nature Made’s Stress Relief gummies

blend L-theanine and chamomile to help you manage stress in the moment, while Nature Made Clear & Focus blends L-theanine and caffeine to reduce mental fatigue and help you focus.

As long as you follow the L-theanine supplement’s dosage suggestions, you can safely take L-theanine daily. And because L-theanine is a 100% drug-free, non-habit-forming ingredient, it is generally considered safe for long-term use. As always, if you’re pregnant, breastfeeding, or taking medication, consult with your doctor before taking any supplements. 

Learn More: Can You Take Melatonin When Pregnant?

What Are The Side Effects Of L-Theanine?

Taking L-theanine produces no direct side effects and is considered safe. However, due to the caffeine content in teas, consuming large amounts can lead to nausea, upset stomach, and irritability. [12]

The Bottom Line

L-theanine is an amino acid naturally found in plant sources such as tea leaves and some mushrooms. L-theanine benefits include helping to support alertness, relaxation, and sleep. The appeal of L-theanine stems from its ability to support a state of alert relaxation, so it can calm you down without causing drowsiness. L-theanine is generally considered safe with no side effects.

Continue to check back on the Nature Made blog for the latest science-backed articles to help you take ownership of your health.

Learn More About Stress & Sleep Supplements:

  • How Long Can You Take Melatonin?
  • What to Eat Before Bed 
  • What is Ashwagandha Good For?
  • This information is for educational purposes only and is not intended to serve as medical advice. Consult your healthcare provider for more information. 

    † These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.


    1. Journal of Agriculture and Food Chemistry. “From Tea Leaves to Factories: A Review of Research Progress in l-Theanine Biosynthesis and Production.” January 21, 2021. Accessed on: January 10, 2022. https://pubs.acs.org/doi/10.1021/acs.jafc.0c06694
    2. Oregon State University’s Linus Pauling Institute. “Green tea.” January 2016. Accessed on: January 10, 2022. https://lpi.oregonstate.edu/mic/food-beverages/tea#reference25
    3. University of California, Santa Cruz. “L-theanine.” June 2013. Accessed on: January 10, 2022. https://healthcenter.ucsc.edu/pharmacy/references/l-%20theanine.pdf 
    4. Huntington College of Health Sciences. “L-Theanine.” 2013. Accessed on: January 11, 2022. https://www.huhs.edu/literature/L-Theanine.pdf 
    5. Psychology Today. “What You Need to Know About L-theanine.” August 29, 2017. Accessed on: January 11, 2022. https://www.psychologytoday.com/us/blog/sleep-newzzz/201708/what-you-need-know-about-l-theanine 
    6. Nutrients. “Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial.” Oct 2019. Accessed on: February 22, 2022. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6836118/ 
    7. Asia Pacific Journal of Clinical Nutrition. “L-theanine, a natural constituent in tea, and its effect on mental state.” 2008. Accessed on: January 11, 2022. https://pubmed.ncbi.nlm.nih.gov/18296328/ 
    8. Journal of the American College of Nutrition. “In Search of a Safe Natural Sleep Aid.” 2015. Accessed on: February 22, 2022. https://pubmed.ncbi.nlm.nih.gov/25759004/ 
    9. Pharmaceutical Biology. “GABA and l-theanine mixture decreases sleep latency and improves NREM sleep.” 2019. Accessed on: January 11, 2022. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6366437/ 
    10. Nutritional Neuroscience. “The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness.” December 2010. Accessed on: January 11, 2022. https://pubmed.ncbi.nlm.nih.gov/21040626/ 
    11. Journal of Physiological Anthropology. “Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses.” 2012. Accessed on: January 11, 2022. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3518171/
    12. Healthline. “What You Should Know About L-Theanine.” January 20, 2021. Accessed on: January 10, 2022. https://www.healthline.com/health/l-theanine#_noHeaderPrefixedContent


    Lisa Beach

    NatureMade Contributor

    Lisa Beach is a seasoned journalist whose work has been published in The New York Times, Good Housekeeping, Eating Well, Parents, AARP’s Disrupt Aging, Optimum Wellness, and dozens more. She also writes for a variety of health/wellness-focused brands. Check out her writer’s website at www.LisaBeachWrites.com.

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    Sandra Zagorin, MS, RD

    Science and Health Educator

    As a member of the Medical and Scientific Communications team, Sandra educates healthcare professionals and consumers on nutrition, supplements, and related health concerns. Prior to joining Pharmavite, Sandra worked as a clinical dietitian at University of Chicago Medicine in the inpatient and outpatient settings. Sandra received her Bachelor of Science degree in Nutritional Science, with minors in Spanish and Chemistry from the University of Arizona in Tucson, AZ. She earned her Master of Science degree in Clinical Nutrition from RUSH University in Chicago, IL. As part of her Master’s program, Sandra performed research on physical activity participation and correlates in urban Hispanic women.

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