L-theanine
BModerate evidenceWhat is L-theanine?
L-theanine is a non-protein amino acid produced by the tea plant, Camellia sinensis, and by a small number of mushrooms. A cup of brewed tea contains roughly 25–60 mg depending on the leaf and the brew, which is why supplement doses of 100–200 mg are several cups worth in a single capsule. Commercially it is either extracted from tea or produced by fermentation; the synthetic form used in most supplements is chemically identical to the tea-derived form.
How it works
L-theanine is structurally similar to glutamate, which lets it cross the blood–brain barrier and interact with glutamate receptors. It is associated with increased alpha-wave activity in the brain — the electrical pattern present during relaxed wakefulness rather than drowsiness — which is the physiological basis for the claim that it produces calm without sedation. It is also proposed to modulate GABA, dopamine and serotonin, though the human evidence for those pathways is much weaker than the marketing implies. Most of what is reliably observed happens alongside caffeine rather than instead of it.
What the research actually shows
Evidence strength varies by what is being claimed, so each use is graded separately against the published criteria rather than averaged into one reassuring letter.
Taken with caffeine, for attention and reduced jitteriness
BModerate evidenceThis is the strongest use and the one most trials actually tested. Combination studies typically pair 100–250 mg of L-theanine with 40–100 mg of caffeine and measure attention-switching tasks and self-reported alertness. The consistent finding is that the combination improves attention more than either alone, and that theanine blunts the unpleasant edge of caffeine. Note what this does not show: a benefit from theanine by itself.
Sources: Haskell CF, Kennedy DO, Milne AL, Wesnes KA, Scholey AB
For subjective stress and relaxation
CLimited evidenceSeveral small trials report reduced self-reported stress and improved sleep quality, generally at 200 mg daily. Sample sizes are small, outcomes are self-reported rather than clinical, and study quality varies. Promising and plausible, but not established, and not comparable to treatment for a diagnosed anxiety disorder.
For memory or long-term cognitive performance
DWeak evidenceThis is where the category marketing runs furthest ahead of the research. Trials measuring memory specifically are few, small, and inconsistent, and an improvement in attention while caffeinated is not evidence of better memory. Any product sold on a memory claim carrying only theanine is making a claim its own ingredient does not support.
Effective dosage
Studied doses cluster at 100–200 mg, most often as a single dose taken with caffeine for acute effects, or 200 mg daily in the stress and sleep trials. Higher intakes have been used in research without notable problems, but there is no evidence that more produces more effect, and the acute studies that found benefits used the lower end of that range.
Where products diverge from the research. The common commercial problem is not underdosing — 100–200 mg per capsule is typical and matches the research. It is what comes with it. Several popular products pair theanine with green tea extract or other actives and market the result as a theanine product, so the panel is worth reading in full rather than trusting the name on the front.
Safety, side effects and interactions
L-theanine is generally well tolerated and has no established serious adverse effects at supplement doses. Because it may modestly lower blood pressure, anyone taking antihypertensive medication should raise it with a clinician. It is often combined with caffeine in commercial products, so the total caffeine from every source is the number that matters for anyone sensitive to stimulants. Safety in pregnancy and breastfeeding has not been established, and it has not been studied adequately in children. It is not a substitute for treatment of a diagnosed anxiety or sleep disorder.
None of this is medical advice. See the medical disclaimer for what that means before you act on anything here.
Products we have covered containing L-theanine
Every label overview on this site whose Supplement Facts panel lists L-theanine, with the amount each one discloses.
NOW L-Theanine 100 mg
A closer look at a relaxation-labelled formula containing both L-theanine and decaffeinated green tea.
Common questions
Does L-theanine work without caffeine?
The evidence is much weaker. Most trials showing a clear cognitive effect gave theanine alongside caffeine and measured the combination. Taken alone, the reliable findings are limited to modest, self-reported changes in stress and relaxation.
How much L-theanine is in a cup of tea?
Roughly 25 to 60 mg, depending on the leaf, quantity and brewing time. A 200 mg capsule is therefore several cups worth in one dose, which is why supplement effects are not directly comparable to drinking tea.
Will L-theanine make me drowsy?
It is not a sedative. The associated increase in alpha-wave activity corresponds to relaxed wakefulness rather than sleepiness, which is the basis for the claim that it produces calm without drowsiness.
Is L-theanine the same as green tea extract?
No, and the distinction matters. Green tea extract is a concentrated preparation containing catechins such as EGCG and carries documented liver-injury reports in some people. L-theanine is a single amino acid with a different and much more benign safety profile. Some products contain both.
Can I take L-theanine every day?
Daily use at 200 mg has been used in trials without notable problems. There is no established reason to cycle it, but there is also no long-term safety data running to years, so open-ended daily use is a judgement call worth raising with a clinician.
References
- Haskell CF, Kennedy DO, Milne AL, Wesnes KA, Scholey AB. The effects of L-theanine, caffeine and their combination on cognition and mood. Biological Psychology, 2008.
- NIH LiverTox: Clinical and Research Information on Drug-Induced Liver Injury — green tea extract entry, relevant where theanine products also contain catechins.
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Last updated 21 September 2026 · Compiled by SNL Team