L-theanine
L-theanine is an amino acid found naturally in green tea.
Camellia sinensis (L.) Kuntze
200 mg a day (range studied: 100–400 mg).
What it is
It is behind the alert calm typical of tea: relaxation without drowsiness. In EEG studies it increases alpha waves, which are associated with a state of wakeful relaxation.
What it is used for
The quiz suggests it when your answers justify it. It usually appears with these goals:
What the evidence says
Trials in people that point the same way, but still few, small or funded by the manufacturer.
Small trials in stressed adults show improvements in feelings of calm and in sleep quality. Consistent results, from small samples.
| Year | What was studied | What was found | Source |
|---|---|---|---|
| 2019 | The most cited RCT on stress and cognition | Crossover RCT, 200 mg a day for 4 weeks: it reduced symptoms of stress and anxiety and improved sleep quality. Funded by an L-theanine producer. | Hidese et al.Nutrients |
| 2024 | The most recent RCT on stress | RCT, 400 mg a day for 28 days: perceived stress and sleep improved, but placebo improved in a similar way, and cortisol did not change. The effect compared with placebo was weak. (Funded by the manufacturer.) | Moulin et al.Neurology and Therapy |
| 2025 | The meta-analysis on cognition | Review of 5 trials: it improved some kinds of mental agility, but not all. | Mátyus et al.Journal of Clinical Medicine |
What to look for on the label
- That the label says the L-theanine comes from tea leaves.
- In the EU only that kind is permitted in supplements: synthetic or fermentation-derived L-theanine (such as Suntheanine®) needs novel food authorisation, and the application is still pending.
Precautions
- It can add to the effect of sedatives and blood pressure medication: if you take them, ask first.
Where to find it
Products whose label meets what this profile asks for: form, dose per serving and nothing that contradicts it. Three at most: quality of the active comes first and, among the best, we look for one option in each price range. We choose by composition, not by who pays. The shops are European or ship to Europe.
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HSNShips from Spain€€Mid rangeEssential Series
L-theanine 250 mg
250 mg of L-theanine from green tea per capsule
For the reference dose1 capsuleView at HSN (opens in a new tab)Meets the criteria. Adds low doses of B5 and B12.
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HSNShips from Spain€BudgetRaw Series
L-theanine powder
Pure L-theanine extracted from green tea
For the reference dose250 mg (one 0.5 ml scoop)View at HSN (opens in a new tab)Meets the criteria.
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ThorneShips from the US: check delivery and customs€€€High endThorne
Theanine
200 mg of L-theanine per capsule
For the reference dose1 capsuleView at Thorne (opens in a new tab)With caveats. The label does not say where the L-theanine comes from.
We link to the shop; we do not sell anything. Today we earn no commission on any link. If we ever do, the link will say so and the selection will not change: the label decides. Labels checked on 2 November 2026; check the one on the pack before you buy. All these shops deliver to the EU; some of their pages open in Spanish. How we are funded.
Nearby in the library
Is it for you?
The quiz decides from your answers, not from a profile.
Profile reviewed on 3 November 2026. Sources: EFSA, Regulation (EU) 432/2012 and published studies. Image: Tea plant (Camellia sinensis). Coloured engraving. Wellcome Collection, public domain.
General information based on published scientific evidence and EU law. Food supplements should not be used as a substitute for a varied, balanced diet and a healthy lifestyle, and are not intended to diagnose, treat or prevent any disease.
Do not exceed the daily dose stated on each product. If you take medication, have a medical condition or have any doubts, ask your doctor or pharmacist.