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Short answer: L-theanine is an amino acid found mainly in tea leaves. It is absorbed well and reaches the brain, and it is popular as a supplement for relaxation, stress and sleep. The research is promising but modest: a systematic review found that 200 to 400 mg a day may help reduce stress in people under stressful conditions, and a 2025 meta-analysis found small improvements in self-reported sleep quality. Tea is the main food source, with roughly 20 mg in a cup of black tea. Independent reviewers caution that the evidence does not yet match the hype.
If you drink matcha or green tea, you already get some L-theanine. It is also sold on its own, often with promises of calm focus and better sleep. Here is what L-theanine is, what the research does and does not show, how much studies used, and how much is in tea and matcha.
What you'll learn
- What L-theanine is and where it comes from
- What the research shows for stress, sleep and focus
- How much L-theanine studies have used
- How much L-theanine is in tea and matcha
What is L-theanine?
L-theanine is an amino acid that occurs naturally in the leaves of the tea plant, Camellia sinensis. Unlike the amino acids that make up proteins, it is not used to build protein (Bulman et al., 2025). It is well absorbed from the gut and can cross the blood-brain barrier, which is why it is studied for effects on mood and the mind (Dashwood & Visioli, 2025). Shading tea plants before harvest, as is done for matcha, increases their theanine content (Kochman et al., 2020).
What is L-theanine good for? What the research shows
| Area | What studies found | How strong is the evidence? |
|---|---|---|
| Stress | A systematic review of 9 randomized trials found that 200 to 400 mg a day may help reduce stress and anxiety in people exposed to stressful conditions (Williams et al., 2020). | Promising but limited; the authors called for longer, larger studies. |
| Sleep quality | A 2025 meta-analysis of 19 trials with 897 people found small improvements in self-reported time to fall asleep, daytime dysfunction and overall sleep quality (Bulman et al., 2025). | Small effects; few studies used pure L-theanine, and the best dose is not known. |
| Relaxed alertness | In a small study, 50 mg increased alpha brain-wave activity, a pattern linked to a relaxed but awake state (Nobre et al., 2008). | Early; the researchers worked for a tea company. |
| Focus with caffeine | Combined with caffeine, L-theanine may improve some measures of attention and alertness (Dashwood & Visioli, 2025). | Mixed; see L-theanine and caffeine. |
| Daily stress and thinking | In a 4-week trial of 30 healthy adults, 200 mg a day improved scores for stress-related symptoms, sleep quality and some thinking tasks (Hidese et al., 2019). | One small trial; two authors worked for the company that supplied the L-theanine. |
An independent 2025 review summed it up: some studies suggest benefits for relaxation, stress and sleep, but findings are often inconsistent, rigorous human trials are lacking, and "the science does not yet match the hype" (Dashwood & Visioli, 2025).
How does L-theanine work?
The exact mechanisms are still being studied (Dashwood & Visioli, 2025). One measurable effect is on brain waves: L-theanine has been shown to increase activity in the alpha frequency band, which researchers describe as relaxing the mind without causing drowsiness (Nobre et al., 2008). That is different from a sedative, which makes you sleepy, and from caffeine, which makes you more alert.
How much L-theanine do studies use?
Studies have used a wide range of doses:
| Amount | Used in |
|---|---|
| About 20 mg | Roughly what a cup of black tea provides (Nobre et al., 2008) |
| 50 mg | Alpha brain-wave study (Nobre et al., 2008) |
| 200 mg a day | 4-week trial in healthy adults (Hidese et al., 2019) |
| 200 to 400 mg a day | Range in stress and anxiety trials (Williams et al., 2020) |
The best dose and how long to take it have not been established (Bulman et al., 2025). Reviewers have urged caution about taking L-theanine supplements at high, drug-like doses until better trials are done (Dashwood & Visioli, 2025). If you use a supplement, follow the label and talk with your provider, especially if you take medication.
How much L-theanine is in tea and matcha?
Tea is the main dietary source. An analysis of 37 commercial teas found an average of about 5 to 6.6 mg of L-theanine per gram of tea leaves, with green tea at about 6.6 mg/g and black tea at about 5.1 mg/g, but the amounts varied widely, and pu-erh tea had practically none (Boros et al., 2016).
| Source | L-theanine (approx.) |
|---|---|
| Cup of black tea | About 20 mg (Nobre et al., 2008) |
| Green tea leaves | About 6.6 mg per gram, on average (Boros et al., 2016) |
| Black tea leaves | About 5.1 mg per gram, on average (Boros et al., 2016) |
| Matcha powder | 9.85 mg per gram in one analysis (Koláčková et al., 2022) |
| Pu-erh tea | Practically none (Boros et al., 2016) |
Because you drink the whole leaf with matcha, a serving can provide more L-theanine than steeped tea, along with caffeine. Supplements usually provide far more than a cup of tea. For more on matcha, see does matcha have caffeine? and matcha benefits.
Is L-theanine safe?
L-theanine has shown a good safety profile in toxicology studies (Dashwood & Visioli, 2025). Still, supplement doses are much higher than what you get from tea, and long-term human data are limited (Dashwood & Visioli, 2025). Talk with your provider before using L-theanine supplements if you are pregnant or breastfeeding, take medication, or have a medical condition.
L-theanine, matcha and coffee
Matcha naturally contains both L-theanine and caffeine, which is one reason people describe it as feeling different from coffee. For how the two compounds interact, see L-theanine and caffeine: why matcha feels different from coffee, and for a side-by-side comparison, see matcha vs coffee.
Common myths (quick reality check)
Myth: L-theanine is a sedative. Reality: L-theanine is linked to a relaxed but awake brain-wave pattern, not drowsiness, in the studies that measured it.
Myth: L-theanine is proven to treat anxiety. Reality: Reviews found it may help reduce stress in people under stressful conditions, but the evidence is limited and inconsistent.
Myth: A cup of tea gives you a supplement dose. Reality: A cup of black tea has about 20 mg, while studies often used 200 to 400 mg a day.
Frequently asked questions (FAQ)
What is L-theanine?
An amino acid found mainly in tea leaves. It is absorbed well, reaches the brain and is sold as a supplement for relaxation, stress and sleep.
What is L-theanine good for?
Research suggests it may help reduce stress in people under stressful conditions and slightly improve self-reported sleep quality, but the evidence is modest.
How much L-theanine should I take?
Studies have used 50 to 400 mg a day, and the best dose is not established. Follow the label and talk to your provider.
Does L-theanine make you sleepy?
Not usually. Studies link it to a relaxed but awake state. Some research found small improvements in sleep quality.
How much L-theanine is in green tea and matcha?
Tea leaves average about 5 to 6.6 mg per gram, and one matcha powder had 9.85 mg per gram. A cup of black tea has about 20 mg.
Is L-theanine safe to take every day?
It has a good safety profile in toxicology studies, but long-term human data on supplement doses are limited. Check with your provider.
Related guides
- When to take L-theanine: morning, night or with coffee?
- L-theanine side effects: is it safe?
- L-theanine and caffeine
- Matcha benefits
- Does matcha have caffeine?
- What is a nootropic?
- What are adaptogens?
Disclaimer and when to seek help
This article is for general education and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Our products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your health care provider before taking L-theanine or other supplements, especially if you are pregnant or breastfeeding, take medication, or have a medical or mental health condition.
References
- Williams JL, 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 for Human Nutrition, 2020;75(1):12-23. doi:10.1007/s11130-019-00771-5
- Hidese S, 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):2362. doi:10.3390/nu11102362
- Bulman A, et al. "The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis." Sleep Medicine Reviews, 2025;81:102076. doi:10.1016/j.smrv.2025.102076
- Nobre AC, Rao A, Owen GN. "L-theanine, a natural constituent in tea, and its effect on mental state." Asia Pacific Journal of Clinical Nutrition, 2008;17 Suppl 1:167-168. PubMed 18296328
- Dashwood R, Visioli F. "l-theanine: From tea leaf to trending supplement - does the science match the hype for brain health and relaxation?" Nutrition Research, 2025;134:39-48. doi:10.1016/j.nutres.2024.12.008
- Boros K, Jedlinszki N, Csupor D. "Theanine and Caffeine Content of Infusions Prepared from Commercial Tea Samples." Pharmacognosy Magazine, 2016;12(45):75-79. doi:10.4103/0973-1296.176061
- Koláčková T, et al. "The effect of in vitro digestion on matcha tea (Camellia sinensis) active components and antioxidant activity." Antioxidants, 2022;11(5):889. doi:10.3390/antiox11050889
- Kochman J, et al. "Health benefits and chemical composition of matcha green tea: a review." Molecules, 2020;26(1):85. doi:10.3390/molecules26010085
