In 30 seconds
- L-theanine is the characteristic amino acid in tea: it makes up 1-2% of the leaf's dry weight, about 25-60 mg per cup.
- In a meta-analysis of 19 trials with 897 people, it improved perceived sleep quality, the feeling of falling asleep sooner and tiredness the next day.
- In a trial with adults averaging 48 years of age, taking it before bed for 4 weeks improved the time taken to fall asleep compared with placebo.
- A review of 9 trials suggests that 200-400 mg a day may help reduce stress and anxiety at times of pressure.
L-theanine is the characteristic amino acid in tea, and it is associated with a relaxed state without drowsiness. In a meta-analysis of 19 trials, it improved perceived sleep quality and tiredness the next day, and other studies have used it for stress and, together with caffeine, for focus. Here is what it is, what has been measured and how much was used.
Tea and studies
The L-theanine in a cup, compared with a trial
What L-theanine is
It is an amino acid found naturally in tea leaves. It makes up 1-2% of their dry weight, about 25-60 mg in a 200 ml cup. A cup of black tea has around 20 mg 3.
To reach the amounts used in many studies you would need several cups: for 200 mg, between 3 and 8, depending on the tea 3. And with them, their caffeine.
How it works: relaxation without sleepiness
In one study, 16 young people took 50 mg of this amino acid dissolved in tea and another 19 took water. Their brain activity was recorded at rest, with their eyes closed, for almost two hours 3.
With L-theanine, alpha waves increased more, between 45 and 105 minutes after taking it. These are the waves typical of a relaxed but awake state, and the authors interpret this as relaxing the mind without causing sleepiness 3.
Sleep meta-analysis
In 19 trials: what people rated more highly
L-theanine and sleep
This is its most studied use. The most recent meta-analysis brought together 19 trials with 897 people, with doses of 50 to 1,000 mg, taken for anything from one night to 8 weeks 1.
With L-theanine, people rated their sleep more highly 1:
- Better sleep quality, in 12 studies.
- The feeling of falling asleep sooner, in 10.
- Less tiredness during the day, in 9.
In objective measurements, such as the actual time taken to fall asleep or sleep duration, there were no significant changes 1. And many of those trials, 11 out of 19, combined it with other ingredients, as night-time formulas do 1.
One of the trials with L-theanine on its own is especially interesting if you are over 40. Thirty adults with an average age of 48 took 200 mg a day before bed for 4 weeks, and placebo for another 4. Compared with placebo, they improved the time taken to fall asleep, sleep disturbances and the use of sleep medication 2.
L-theanine and stress
In that same trial, during the 4 weeks with L-theanine, scores for baseline anxiety and low mood fell compared with the start 2. It is the bridge between daytime stress and sleep, which we explain in stress and sleep.
A review of 9 trials with L-theanine on its own concluded that 200-400 mg a day may help reduce stress and anxiety in people going through situations of pressure. Its authors call for longer and larger studies 4.
By day and by night
Two studied uses of L-theanine
L-theanine and caffeine
This is the other side of L-theanine, the daytime one. In a trial with 27 adults who drank coffee every day, L-theanine (100 mg) together with 50 mg of caffeine improved speed and accuracy when switching tasks at 60 minutes. It also reduced distraction at 60 and 90 minutes, something caffeine alone did not achieve 5.
At night, of course, caffeine is best left out: you will find how many hours to allow in caffeine and sleep. For sleep, L-theanine without coffee.
How much is used in the studies
| Study | Amount and timing | Result |
|---|---|---|
| Nobre et al., 2008 | 50 mg, in a single dose | More alpha waves between 45 and 105 minutes later |
| Owen et al., 2008 | 100 mg together with 50 mg of caffeine | Faster and more accurate task switching, and less distraction |
| Hidese et al., 2019 | 200 mg a day before bed, 4 weeks | Shorter time to fall asleep, fewer sleep disturbances and less use of sleep medication |
| Williams et al., 2020 | 200-400 mg a day | May help reduce stress and anxiety in situations of pressure |
| Bulman et al., 2025 | 50-1,000 mg, from 1 night to 8 weeks | Better perceived sleep quality and less daytime tiredness |
Sources: Nobre et al., 2008; Owen et al., 2008; Hidese et al., 2019; Williams et al., 2020; Bulman et al., 2025.
What we do not know yet
- The ideal dose. Trials with similar amounts and durations gave different results, and the authors of the meta-analysis call for a trial comparing doses 1.
- The effect on its own. Few studies use L-theanine alone; most combine it with other ingredients 1.
- The long term. For stress, longer studies are needed, including with the L-theanine you get from tea 4.
- The ratio with caffeine. The focus trial used more L-theanine than caffeine, the opposite of a cup of tea 5.
Tea or supplement
One or two cups of tea a day give you some L-theanine, about 25-60 mg per cup 3. It is a good habit in the morning or mid-afternoon.
For the evening, the maths changes: the amounts in the sleep trials call for several cups, and with them comes caffeine. That is why, for sleep, it makes more sense to take it without tea, in a formula designed for that time of day.
Is it safe?
In the 4-week trial there were no side effects, and blood tests did not change 2. If you are pregnant or breastfeeding, take medication or have a medical condition, check with your doctor.
You will find the sleep data, with their level of evidence, in L-theanine and tryptophan: what the studies say.
Frequently asked questions
What is L-theanine good for?
It is the characteristic amino acid in tea and is associated with a relaxed state without drowsiness. In studies it has been used for better sleep, for stress and, together with caffeine, for focus.
How much L-theanine do you take for sleep?
Studies have used 50 to 1,000 mg. One of the most cited trials gave 200 mg a day before bed for 4 weeks.
Does L-theanine make you sleepy?
Not like a sedative. In one study it increased alpha brain waves, typical of a relaxed but awake state, and in others it has been taken during the day together with caffeine.
How much L-theanine is in a cup of tea?
Between 25 and 60 mg per 200 ml cup, according to a review: it makes up 1-2% of the leaf's dry weight. A cup of black tea has around 20 mg.
Can you take L-theanine with coffee?
Yes, it is a well-studied combination. In one trial, L-theanine (100 mg) with 50 mg of caffeine improved speed and accuracy in an attention task more than caffeine alone.
Sources
- Bulman A, et al. The effects of L-theanine consumption on sleep outcomes: a systematic review and meta-analysis. Sleep Med Rev. 2025;81:102076. View publication
- 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. View publication
- 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(Suppl 1):167-168. View publication
- 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. View publication
- 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):193-198. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
