L-Theanine

L-theanine · theanine

The green-tea amino acid promoted for calm alertness and better sleep.

TypeSupplement / dietary

The grade answers: What does the human evidence support for: Calm focus & sleep?

Grade

Limited

The grade rates evidence quality — it is not advice to take or buy.

Class: Amino acid
Primary use: Calm focus & sleep
Evidence strength: low
Last reviewed: 2026-07-01

Bottom line

A safe, mild relaxant with modest evidence for 'calm focus' — especially paired with caffeine. Not a longevity molecule, but one of the more honest small-benefit supplements.

What the evidence says

L-theanine has small human trials suggesting it reduces subjective stress and, combined with caffeine, improves attention while smoothing caffeine's jitteriness. Some evidence points to better sleep quality (via relaxation rather than sedation). The effects are modest and short-term, and there is no aging or longevity outcome data. Grade C: a legitimate, low-risk 'calm without drowsiness' aid, not a healthspan intervention.

Key studies

[1]
L-theanine and caffeine on attention · RCT
Improved attention and reduced caffeine jitter in combination.
Open on PubMed ↗
[2]
L-theanine, stress and sleep · review
Modest reductions in stress; sleep-quality signals.
Open on PubMed ↗
[3]
L-theanine pharmacology (review) · review
Explains the 'calm alertness' mechanism.
Open on PubMed ↗

See all studies on PubMed ↗

Scoped PubMed search, not a curated bibliography: the individual PMIDs for this entry have not yet been verified one by one. For that reason it is not used to support a high grade and is awaiting review.

Mechanism

Crosses the blood-brain barrier and modulates neurotransmitters (increasing GABA, serotonin, dopamine and alpha brain-wave activity), producing relaxation without sedation.

Safety

Very well tolerated; no significant safety concerns at studied doses. Naturally present in tea. May mildly lower blood pressure.

Dosage context

Trials commonly use ~100–200 mg, often alongside ~100 mg caffeine for the focus effect. A cup of green tea provides much less.

Examples of application

Taken ~100–200 mg, often with caffeine for calm focus.
Also used before bed for relaxation without sedation.
A gentle, low-risk 'nice to have', not a longevity active.

From the field

L-theanine is a rare supplement whose modest, honest claim roughly matches its modest, honest evidence. We grade it C and keep it in the 'nice, low-risk, not magic' bucket.

Related molecules

AshwagandhaC MagnesiumC

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