What L-theanine does in your body and how much to take
Updated · 10 studies cited · 5 products compared
Short answer
L-theanine comes from tea and works fast. About an hour after you take it, your brain shifts toward a calm but awake state, and you may react a bit faster. It may ease stress a little, but the studies don't all agree.
- What it helps
- Staying focused. It may also help you feel a bit calmer when you are stressed.
- How much
- 200 mg, 30 to 60 minutes before you need it. Most studies stayed between 200 and 400 mg a day.
- How long
- Within about an hour.
- How sure are we
- Some proof
- Skip it or ask first
- Ask your doctor first if you are pregnant, breastfeeding, or take medicine for blood pressure or mental health.
See details
L-theanine is an amino acid from tea that acts on the brain quickly. Within about an hour it raises alpha activity on EEG,2 and a single 200 mg dose improved reaction time in healthy adults.1 It may calm the body's response to stress, but the studies disagree.34
200 to 400 mg a day in most studies.10 A single 200 mg dose 30 to 60 minutes beforehand in attention studies1
Ask first if you are pregnant, breastfeeding, or on blood pressure or psychiatric medication.
How does L-theanine work in your body?
Your brain cells talk using tiny electric signals. After L-theanine, these signals shift to a pattern seen when people are relaxed but awake. It also seems to block a brain chemical that revs brain cells up. That may be why it feels calming without making you sleepy.
See details
EEG recordings show more activity in the alpha band after L-theanine, a pattern researchers link with a relaxed but awake state. Two studies saw this after only 50 mg, which is more than a cup of black tea provides (about 20 mg).2 L-theanine also blocks glutamate from binding to its receptors in the brain, which may explain part of the calming effect.3
Alpha activity was tracked from 45 to 105 minutes after the dose.
What does L-theanine do, and how much does it help?
Most of this was measured within a few hours of one dose, often in healthy young adults.
Focus and reaction time
Helps clearlyThis is the best result. One 200 mg dose helped healthy people react faster on tests. People short on sleep also paid attention better when they took a high dose, or took it with caffeine.
How long: 30 to 60 minutes after you take it.
See details
Strong proof
This is the most consistent result. A 2026 meta-analysis of 31 trials and 1,168 people found that a single 200 mg dose improved choice reaction time, with a standardized effect of 0.51.1 In sleep-deprived adults, attention in a traffic-scene task also improved with a high dose,9 and with 200 mg of L-theanine plus 160 mg of caffeine.8
The dose was taken 30 to 60 minutes before testing.
Feeling stressed or worried
Helps a littleIt may lower stress and worry a little. Much of that effect came from the weaker studies, so the real effect may be smaller.
How long: Studies ran from one dose to about 8 weeks.
See details
Some proof
A review of nine studies suggested that 200 to 400 mg a day may lower stress and anxiety in people under stressful conditions.5 The 2026 meta-analysis was less enthusiastic. It found a modest reduction in acute stress (effect size 0.31), and studies at high risk of bias accounted for much of it.1
Studies range from one dose to about 8 weeks.
Heart rate under stress
Not sure yetIn one small study, the heart sped up less under stress. A later, more careful study found no change.
See details
Little proof
In a small crossover study of 12 people doing mental arithmetic, heart rate and salivary immunoglobulin A rose less after L-theanine, which the authors attributed to lower sympathetic nervous activity.3 A pre-registered 2024 trial did not reproduce this. It found no effect on heart rate or salivary stress markers during a mental stress challenge.4 We would treat this one as unsettled.
Sleep
Not sure yetIn one small study, people said they slept better and fell asleep faster after 4 weeks. That is not enough to call it a sleep aid.
How long: 4 weeks in that study.
See details
Little proof
Thirty adults without major psychiatric illness took 200 mg a day for four weeks, and their sleep quality scores improved compared with baseline, including the time taken to fall asleep and sleep disturbance.6 That is one small trial using self-reported sleep. We don't think it shows L-theanine treats insomnia.
Four weeks in that trial.
Mood
Not sure yetThere is a small hint it may lift mood for a short time in healthy people. We need better studies.
See details
Little proof
The 2026 meta-analysis saw a possible short-term drop in depressive symptoms in healthy people after excluding one outlier study, and its authors asked for better trials in patients.1
Should you take L-theanine with caffeine?
Taking it with caffeine helped focus and mood a little for about two hours. Some of that help came from the caffeine. Many studies used far more than you would get from drinking tea.
See details
A 2025 review covered 50 trials of tea, theanine, and caffeine. Theanine plus caffeine produced small to moderate benefits for cognition and mood over the first two hours.7 Caffeine accounts for at least part of this, and many of the doses were far above what you'd get by drinking tea.
How much L-theanine should you take?
One 200 mg capsule matches the focus studies. Two capsules reach 400 mg, the top of the usual range. Studies call this safe for up to 8 weeks. We don't have good data on longer use.
See details
Doses of 200 to 400 mg a day have been described as safe for up to 8 weeks.10 We couldn't find good long-term safety data beyond that. A 200 mg capsule matches the attention studies, and two of them reach the top of the usual range.
Best L-theanine supplements by study dose and cost a day
Capsules with 200 mg come first. If they tie, the one with more reviews comes first.
Cost a day is for 200 mg a day, the amount from the focus studies.
| Product | Cost a day | Lasts |
|---|---|---|
| Nutricost, L-Theanine, 200 mg, 120 Capsules1 capsule a day | $0.10Lowest | 120 days |
| Force Factor, L-Theanine, 200 mg, 60 Vegetarian Capsules1 capsule a day | $0.12 | 60 days |
| NOW Foods, L-Theanine, 120 Veg Capsules1 capsule a day | $0.18 | 120 days |
| California Gold Nutrition, L-Theanine with AlphaWave, 200 mg, 60 Veggie Capsules1 capsule a day | $0.18 | 60 days |
| Sports Research, L-Theanine, 200 mg, 60 Softgels1 soft capsule a day | $0.35 | 60 days |
-
1
California Gold Nutrition, L-Theanine with AlphaWave, 200 mg, 60 Veggie Capsules
1 capsule: 200 mg L-theanine
The same amount as the focus studies.
View on iHerb$0.18 a day
1 capsule a day
$11.07 on iHerb for 60 days -
2
Nutricost, L-Theanine, 200 mg, 120 Capsules
1 capsule: 200 mg L-theanine
The same amount. Two capsules reach 400 mg.
View on iHerb$0.10 a day Lowest cost here
1 capsule a day
$11.95 on iHerb for 120 days -
3
Sports Research, L-Theanine, 200 mg, 60 Softgels
1 softgel: 200 mg L-theanine
The same amount in a soft capsule.
View on iHerb$0.35 a day
1 soft capsule a day
$20.97 on iHerb for 60 days -
4
Force Factor, L-Theanine, 200 mg, 60 Vegetarian Capsules
1 capsule: 200 mg L-theanine
The same amount in a vegetarian capsule.
View on iHerb$0.12 a day
1 capsule a day
$6.99 on iHerb for 60 days -
5
NOW Foods, L-Theanine, 120 Veg Capsules
1 capsule: 200 mg L-theanine + 100 mg inositol
The same amount, plus added inositol, which these studies did not test.
View on iHerb$0.18 a day
1 capsule a day
$21.72 on iHerb for 120 days
Amounts and US prices come from each product's iHerb page on November 6, 2026. Prices change often and differ by country, so check the current price on iHerb. Shipping and tax are not included. How we rank products
Common questions
How long does L-theanine take to work?
About 30 to 60 minutes.
Will L-theanine make me sleepy?
Studies describe feeling relaxed, not drowsy. People differ, so try your first dose when you don't need to drive.
See details
The EEG work describes relaxation without drowsiness.2 Individual reactions can differ, so we'd try the first dose at a time when you don't need to drive.
Is it safe to take every day?
Studies call 200 to 400 mg a day safe for up to 8 weeks. We don't know much about longer use.
See details
A review describes 200 to 400 mg a day as safe for up to 8 weeks.10 Longer use hasn't been studied much.
Do I get the same effect from green tea?
Probably less. A cup of black tea has about 20 mg. Most studies used 200 mg.
See details
Probably less. A cup of black tea has about 20 mg,2 well below the 200 mg in most capsule studies.
Who should not take L-theanine?
- Pregnant or breastfeeding: we don't know enough about safety, so talk to your doctor.
- Blood pressure medicine: ask first, in case the two add up.
- Medicine for mental health: talk to the doctor who prescribes it first.
- We know less about safety after 8 weeks.
Studies we used
See all 10 studies
- Meta-analysis or review
31 trials, 1,168 people. A 200 mg dose improved attention; stress reduction was modest and influenced by risk of bias.
Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials. Mol Psychiatry, 2026. PubMed 42410082
- Clinical trial
EEG in healthy young adults after 50 mg. Alpha activity rose compared with placebo.
L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr, 2008. PubMed 18296328
- Clinical trial
12 people under mental stress. Heart rate and salivary IgA responses were lower.
L-Theanine reduces psychological and physiological stress responses. Biol Psychol, 2007. PubMed 16930802
- Clinical trial
Pre-registered 2024 trial. No effect on stress markers during a mental stress challenge.
Impact of L-theanine and L-tyrosine on markers of stress and cognitive performance in response to a virtual reality based active shooter training drill. Stress, 2024. PubMed 38975711
- Meta-analysis or review
9 studies. 200 to 400 mg a day may reduce stress and anxiety under stressful conditions.
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. PubMed 31758301
- Clinical trial
30 adults, 200 mg a day for four weeks. Stress-related and sleep scores improved.
Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients, 2019. PubMed 31623400
- Meta-analysis or review
50 trials on tea, theanine, and caffeine. Small to moderate short-term benefits.
Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutr Rev, 2025. PubMed 40314930
- Clinical trial
37 sleep-deprived adults. 200 mg L-theanine with 160 mg caffeine improved attention.
High-dose L-theanine-caffeine combination improves neurobehavioural and neurophysiological measures of selective attention in acutely sleep-deprived young adults: a double-blind, placebo-controlled crossover study. Br J Nutr, 2025. PubMed 40789769
- Clinical trial
Sleep-deprived adults. High-dose L-theanine improved selective attention.
Effect of L-theanine on selective attention in a traffic-related reaction task in sleep-deprived young adults: a double-blind placebo-controlled, crossover study. Nutr Neurosci, 2025. PubMed 39052627
- Guideline or expert review
Clinical review. 200 to 400 mg a day for up to 8 weeks described as safe.
Psychotropic effects of (L)-theanine and its clinical properties: From the management of anxiety and stress to a potential use in schizophrenia. Pharmacol Res, 2019. PubMed 31412272