From Anirva, the maker of Sleep Harmony. This article is general information, not medical advice. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.
Some nights, the body is tired but the mind keeps going. It replays the day, plans tomorrow and will not settle. If that sounds familiar, you may have come across L-theanine, a calming amino acid found in tea. Here we look at what L-theanine is, what the sleep research found, and how much is in Sleep Harmony.
In this article
Key Takeaways
- L-theanine comes from tea. A cup of black tea has about 24 mg, and a cup of green tea about 8 mg.
- Recent reviews found modest sleep benefits. A 2025 analysis of 18 trials found small improvements in how people rated their sleep.
- The studied amount matches Sleep Harmony. Many trials used 200 mg a day, and Sleep Harmony contains 200 mg.
- It was well tolerated in studies. No significant side effects were reported in a 4-week trial at 200 mg a day.
- Sleep Harmony has no caffeine. Tea contains caffeine, which can make sleep harder.
What Is L-Theanine?
L-theanine is an amino acid, one of the building blocks found in foods. It occurs naturally in tea leaves.
The amount in a cup of tea depends on the type of tea and how long it brews. In one study, a standard 200 ml cup of black tea contained about 24 mg of L-theanine. A cup of green tea contained about 8 mg [5]. Brewing time made a big difference. Adding a little milk or sugar did not [5].
Tea also contains caffeine. MedlinePlus lists 60 to 100 mg of caffeine in a 16-ounce cup of black or green tea [6]. It notes that caffeine can cause trouble sleeping [6]. This is one reason sleep supplements use L-theanine on its own, without the tea.
How Might L-Theanine Help With Sleep?
Researchers are still studying how L-theanine works. In a small study of 35 healthy young adults, 50 mg of L-theanine increased alpha brain-wave activity more than placebo did [10]. The researchers explain that this pattern suggests a relaxed mind without drowsiness [10]. One of the authors worked for a company that sells tea products [10].
A 2015 review suggests that 200 mg of L-theanine before bed may support sleep quality by easing a busy mind, not by sedation [12].
L-theanine is absorbed fairly quickly. In a study of 25–100 mg taken as tea or in water, blood levels peaked about 50 minutes later [4].
What Does the Research Show?
The research on L-theanine and sleep is still growing, and most of the results so far are modest. Memorial Sloan Kettering describes the human data as limited, with small studies suggesting better sleep [13]. Two reviews published in 2025 pulled the studies together.
The 2025 reviews
The larger review included 19 studies with 897 people and pooled the results of 18 of them [1]. Compared with placebo, L-theanine gave small improvements in how quickly people felt they fell asleep. The improvement in overall sleep-quality scores was somewhat larger, and people also reported feeling better during the day [1]. The authors call for more studies of L-theanine on its own [1].
A second review looked at 13 trials with 550 people. The amounts ranged from 50 to 900 mg a day [2]. The authors found improvements in time to fall asleep, staying asleep and feeling refreshed on waking. Most of these were randomized trials. Some measured sleep with objective tests as well as questionnaires [2]. The authors found improvements in both kinds of measures [2]. They concluded that 200 to 450 mg a day appears to be a safe way to support healthy sleep in adults [2]. They also call for larger, higher-quality trials, including studies in people with long-term sleep problems [2].
A 4-week trial in healthy adults
This trial included 30 healthy adults, 21 women and 9 men, with an average age of 48 [3]. Each person took 200 mg of L-theanine a day for four weeks and a placebo for four weeks, in random order, with a two-week break in between. Overall sleep scores improved after L-theanine [3]. Compared with placebo, people fell asleep faster and reported fewer sleep disturbances [3]. The study was funded by Taiyo Kagaku, which makes L-theanine and supplied the tablets [3].
What a review found for stress
A 2020 review looked at nine trials of L-theanine supplements [11]. It suggests that 200 to 400 mg a day may help reduce stress in people facing stressful situations. The authors call for longer and larger studies [11].
Study summary
| Study | People | Amount a Day | Length | Main Result |
|---|---|---|---|---|
| Bulman et al., 2025 (review) | 19 studies, 897 people (18 pooled) | Varied | Varied | Small improvements in self-rated time to fall asleep, sleep quality and daytime function vs placebo. |
| Cotter et al., 2026 (review) | 13 trials, 550 people | 50–900 mg | Varied | Improvements in sleep measures; 200–450 mg a day suggested for adults. |
| Hidese et al., 2019 | 30 healthy adults | 200 mg | 4 weeks | Faster sleep onset and fewer sleep disturbances vs placebo. |
| Williams et al., 2020 (review) | 9 trials | 200–400 mg suggested | Varied | May help reduce stress in people facing stressful situations. |
How Much L-Theanine Is in Sleep Harmony Compared With the Studies?
| Source | L-theanine a Day | Notes |
|---|---|---|
| Sleep Harmony (2 capsules) | 200 mg | From the label |
| 4-week trial | 200 mg | Healthy adults |
| 2025 review, suggested range | 200–450 mg | For adults |
| Cup of black tea | About 24 mg | Standard 200 ml cup |
| Cup of green tea | About 8 mg | Standard 200 ml cup |
What the Research Does Not Show Yet
Many trials are small, and many rely on how people rate their own sleep.
Some trials used L-theanine together with other ingredients, so the reviewers ask for more studies of L-theanine alone [1].
We found no study of L-theanine together with melatonin, so we cannot say how the two work together.
L-theanine is not designed to make you drowsy. In the brain-wave study, it produced a relaxed state without drowsiness [10]. So it may suit a busy, restless mind more than it suits simple tiredness.
Safety and Interactions
Memorial Sloan Kettering Cancer Center notes that no side effects have been reported from L-theanine supplements [13]. It also notes that L-theanine does not appear to affect the liver enzymes that process many medicines [13].
Most L-theanine studies lasted a few weeks, so less is known about use over many months [1][2]. In animal safety testing, no harmful effects were seen even at very high amounts, above 2,000 mg per kg of body weight a day [12].
Memorial Sloan Kettering advises talking with a healthcare provider before use during pregnancy or breastfeeding, because L-theanine may not be safe then [13].
L-Theanine Is One Part of Sleep Harmony
Sleep Harmony combines melatonin, calming herbs and three probiotics in one formula. We chose ingredients that have each been studied for relaxation and sleep. L-theanine is one of them.
Sleep Harmony has not been clinically tested as a finished product. For this reason, we cannot say how its ingredients work together. The studies in this article tested L-theanine by itself, and their results describe L-theanine alone.
If you take Sleep Harmony, you are not relying on L-theanine alone. It is one of 14 ingredients in each serving.
Good to Know
If You Are Deciding
L-theanine is one part of a bigger picture. Cleveland Clinic suggests a steady sleep schedule, less caffeine and alcohol, and a cool, dark bedroom. It also suggests putting screens away before bed [8].
If you enjoy tea in the evening, keep in mind that most tea also contains caffeine [6]. If you would like to try Sleep Harmony, the directions are two capsules 30 to 60 minutes before bedtime [7].
The Short Version
L-theanine is an amino acid from tea that is studied for calm and sleep. Two 2025 reviews found modest improvements, mostly in how people rated their own sleep. Many trials used 200 mg a day, the same amount as in Sleep Harmony. In Sleep Harmony, L-theanine works alongside 13 other ingredients.
Frequently Asked Questions
Does L-theanine help you sleep?
How much L-theanine is used for sleep?
What is the difference between L-theanine and melatonin?
Can you take L-theanine and melatonin together?
When do people usually take L-theanine for sleep?
How long does L-theanine take to work?
Is L-theanine safe to take every night?
Does L-theanine help with stress and sleep?
Does L-theanine make you sleepy?
Can I get enough L-theanine from tea?
What is the difference between L-theanine and GABA?
References
- Bulman A, D'Cunha NM, Marx W, Turner M, McKune A, Naumovski N. The effects of L-theanine consumption on sleep outcomes: a systematic review and meta-analysis. Sleep Med Rev. 2025;81:102076. doi:10.1016/j.smrv.2025.102076.
- Cotter J, Caddick CE, Harper JL, Ebajemito JK. Examining the effect of L-theanine on sleep: a systematic review of dietary supplementation trials. Nutr Neurosci. 2026;29:224–238. doi:10.1080/1028415X.2025.2556925.
- Hidese S, Ogawa S, Ota M, Ishida I, Yasukawa Z, Ozeki M, Kunugi H. 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. PMID 31623400.
- van der Pijl PC, Chen L, Mulder TPJ. Human disposition of L-theanine in tea or aqueous solution. J Funct Foods. 2010;2(4):239–244.
- Keenan EK, Finnie MDA, Jones PS, Rogers PJ, Priestley CM. How much theanine in a cup of tea? Effects of tea type and method of preparation. Food Chem. 2011;125:588–594. doi:10.1016/j.foodchem.2010.08.071.
- MedlinePlus Medical Encyclopedia. Caffeine in the diet. U.S. National Library of Medicine. Reviewed April 1, 2025. medlineplus.gov
- Anirva. Sleep Harmony with Probiotics: Supplement Facts label and product page. anirva.com/products/sleep-harmony (accessed September 30, 2026).
- Umeda N (expert). Does magnesium help you sleep better? Cleveland Clinic Health Essentials. September 4, 2026. health.clevelandclinic.org
- Cleveland Clinic. Melatonin: what it is, what it does and how it works. Reviewed April 28, 2025. my.clevelandclinic.org
- Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. 2008;17(S1):167–168. PMID 18296328.
- Williams JL, Everett JM, D'Cunha NM, Sergi D, Georgousopoulou EN, Keegan RJ, McKune AJ, Mellor DD, Anstice N, Naumovski N. 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. 2020;75:12–23. doi:10.1007/s11130-019-00771-5. PMID 31758301.
- Rao TP, Ozeki M, Juneja LR. In search of a safe natural sleep aid. J Am Coll Nutr. 2015;34(5):436–447. doi:10.1080/07315724.2014.926153. PMID 25759004.
- Memorial Sloan Kettering Cancer Center. About Herbs: L-theanine. mskcc.org (text supplied by Sabu Varghese, September 30, 2026).
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