L-Theanine
An amino acid from tea leaves, taken above all for calm and sleep.
- Calm and stress
- Sleep
- Focus and attention
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
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On this page
What is L-Theanine?
L-theanine is an amino acid that the tea plant, Camellia sinensis, makes in its leaves, alongside caffeine and the polyphenols green tea is known for. It is a non-protein amino acid, which means the body does not use it to build its own proteins; in shape it sits closer to glutamine, an amino acid the brain handles constantly, than to anything in a protein powder. Supplements sell it on its own, without the caffeine, as capsules, tablets or powder. Interest in it has risen sharply over the past few years, almost all of it around relaxation and concentration.
Why do people take L-Theanine?
Calm and stress
The thinking. This is the reason most people reach for it: a quieter head after a hard day, or before something they are dreading. The appeal is calm without drowsiness, relaxation without sedation as reviewers put it, and that is what sets theanine apart from the things people take to bring on sleep.
What research has found. Two reviews have pooled the randomised trials. An earlier one, covering nine trials of 200 to 400 mg a day in people put under stress, concluded that stress and anxiety scores came down. A 2026 review of thirty-one trials in about 1,170 adults found the fall in stress after a single dose only modest, and weighted towards trials it judged at high risk of bias, with uneven results for anxiety; the clearest short-term signal it picked up was on attention instead. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
Sleep
The thinking. Theanine’s other everyday use is at bedtime, often by the same people who take it for stress, and it is a familiar ingredient in evening formulas. The thinking is not sedation but a quieter mind: reviewers describe it as aiding relaxation without knocking people out, so the hope is that sleep arrives more easily on its own.
What research has found. A 2025 meta-analysis of eighteen trials in 897 people found small average gains in how quickly people said they fell asleep, in overall sleep quality, and in how they felt the following day. A 2026 review of thirteen trials in 550 adults, all of them using theanine on its own at 50 to 900 mg a day, reported gains on both measured and self-reported sleep, mostly in ordinary poor sleepers rather than people diagnosed with insomnia. A fair body of trials has looked at this, and most point the same way.
Focus and attention
The thinking. A third group take theanine to concentrate, very often alongside caffeine. The pairing is common enough that researchers have tested the two separately and together for years, and reviewers report that the combination has been linked to better attention and alertness than either on its own. What makes the idea work at all is that theanine is described as calming without dulling thinking.
What research has found. Three small crossover trials have measured attention in healthy adults and athletes. A 200 mg drink produced faster responses to on-screen targets than a placebo in a group of nine men, and a trial in twenty-seven young adults found the brain’s attention response quickened at the largest dose tested, 400 mg, with the effect rising as the dose rose. A third, in elite curlers, gave theanine alone, caffeine alone and the two together, but reported its results for the combination, so what theanine did by itself there is not clear from it. Research here is still young: a few studies so far, mostly pointing the same way.
What does L-Theanine do in the body?
Theanine is absorbed readily from the gut and, reviewers report, can cross into the brain itself rather than working at a distance. Once there it has been linked in some studies to a rise in the brain’s alpha waves, the electrical rhythm that shows up when someone is relaxed but wide awake. That pattern is the usual explanation offered for the calm-but-alert quality people describe, though reviewers add that the findings are not consistent.
The longer version starts with its shape. Theanine looks very like glutamine, one of the amino acids the brain handles in quantity, and work in cultured brain cells shows it competing for the transporters that carry glutamine into them, with knock-on effects on the signals that govern cell growth. Reviewers are careful to say that much of this sits in animal and cell studies rather than in people, and that long-term human data are thin.
What do people say about taking L-Theanine?
These are anecdotes people have shared, not evidence.
What people like
- Calm rather than sleepiness is the commonest report: a steadier head, and less alarm at symptoms, while the day carries on as normal.
- Women around the menopause mention it often for night-time anxiety, usually taken with magnesium at bedtime alongside whatever else they are already using.
- Some take it for clarity and concentration rather than calm, and say it is one of the few things in their routine they can actually feel.
- A few pair it with the morning coffee to take the edge off the caffeine, and say that particular combination suits them well.
Common complaints
- Noticing nothing is a common outcome: physical symptoms of anxiety and sleep unchanged, and a few people stop again within a day or two.
- A minority describe feeling briefly unwell rather than calm, with light-headedness in the hour after a capsule the example that comes up.
- Whether it sits with prescribed antidepressants is the question that recurs most, and the threads end in uncertainty rather than any settled answer.
- Several arrive already disappointed by other sleep remedies, so expectations are low, and a single unremarkable night is often enough to end the trial.
How people take it
- Single capsules of 100 mg or 200 mg are what people describe taking; almost nobody in these threads works up to a larger amount.
- Timing follows the purpose: evening or bedtime when the aim is anxiety or sleep, morning with coffee when the aim is concentration.
- It is very commonly taken alongside something else, magnesium most often, and sometimes at a reduced amount beside prescribed medication or hormone replacement.
- Most take it when they feel they need it rather than daily, and describe judging it within an hour or two rather than over weeks.
Read from these public discussions:
- L-theanine (Patient.info, 2018)
- L-Theanine put to the test right now (Patient.info, 2020)
- Sertraline and l theanine? (Patient.info, 2015)
- Caffeine reduction (Mumsnet, 2023)
- Menopause natural supplements to ease anxiety (Mumsnet, 2025)
- What is your supplement regime? (Mumsnet, 2025)
What forms of L-Theanine are there?
| Form | What’s different | Per serving, on products we list |
|---|---|---|
| L-theanine | The amino acid on its own, the same one tea leaves carry, without the caffeine that comes with them. | 200 mg |
What else is worth knowing about L-Theanine?
- Labels give the amount per serving, and a serving may be more than one capsule; the trials behind these reviews used 50 to 900 mg a day, most often 200 to 450 mg.
- Some trials gave a single dose half an hour to an hour before a task, others a daily dose for weeks; reviewers say the dose and the length of time that suit a given purpose have not been settled.
- The largest review compared how many people left the theanine and placebo groups and why, and reported no serious adverse events; a review of the toxicology reports a good safety profile, while noting that long-term human data are limited.
- Reviewers of the sleep trials point out that many of them used theanine inside a blend rather than on its own, and that few have been run in people diagnosed with insomnia.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (13 studies)
- Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials. (2026, systematic review)
- The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review. (2020, systematic review)
- Examining the effect of L-theanine on sleep: a systematic review of dietary supplementation trials. (2026, systematic review)
- The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis. (2025, meta-analysis)
- Effect of single or combined caffeine and L-Theanine supplementation on shooting and cognitive performance in elite curling athletes: a double-blind, placebo-controlled study. (2023, randomised trial)
- L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover study. (2022, randomised trial)
- l-Theanine and caffeine improve target-specific attention to visual stimuli by decreasing mind wandering: a human functional magnetic resonance imaging study. (2018, randomised trial)
- Green tea (Camellia sinensis) and l-theanine: Medicinal values and beneficial applications in humans-A comprehensive review. (2017, review)
- l-theanine: From tea leaf to trending supplement - does the science match the hype for brain health and relaxation? (2025, review)
- Nutritional applications and beneficial health applications of green tea and l-theanine in some animal species: A review. (2020, review)
- An L-Glutamine Transporter Isoform for Neurogenesis Facilitated by L-Theanine. (2017, review)
- Cystine and theanine: amino acids as oral immunomodulative nutrients. (2013, review)
- The Emerging Role of Citrulline and Theanine in Health and Disease: A Comprehensive Review. (2025, review)
How much does L-Theanine cost?
That depends on the form and the pack, so we work out the price of the same dose of every L-Theanine product we can find and rank them.