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Amino acid

L-Theanine

L-theanine is an amino acid found in tea leaves that is not used to build proteins. Black and green tea contain it alongside caffeine.

Also listed as Theanine

Stress & MoodSleepCognition

What it is studied for

The strongest rated effects first. Bars show the size of the effect, the letter grades the evidence, and each rating lists the studies behind it.

StressStress & MoodModerateA3 studies
Sleep qualitySleepModerateB3 studies
Mood SupportStress & MoodModerateBNo linked study
AnxietyStress & MoodModerateB3 studies
Cortisol stressStress & MoodSmallB3 studies
Focus And AttentionCognitionSmallB3 studies
All 7 rated effectsGrouped by health goal, with the publications behind each rating

What is L-theanine?

L-theanine is an amino acid in tea leaves, but it is not a building block for proteins. Black and green tea contain it alongside caffeine; an isolated theanine tablet changes that combination. 1

Why might it affect relaxation?

Theanine resembles glutamate, a chemical involved in nerve signaling. Laboratory and animal research suggests effects on glutamate receptors and other brain signaling systems, while human experiments have examined electrical brain activity. These are clues to a possible mechanism, not a direct measure of how calm someone feels. 2

Key studies

The most recent publications linked to L-Theanine's ratings.

Safety and Efficacy of AlphaWave® l-Theanine Supplementation for 28 Days in Healthy Adults with Moderate Stress: A Randomized, Double-Blind, Placebo-Controlled Trial2024Effect of a nutraceutical combination on sleep quality among people with impaired sleep: a randomised, placebo-controlled trial2024The Effects of L-Theanine Supplementation on Quality of Sleep: A Systematic Review2023Dose–response effect of L-theanine on psychomotor speed, sustained attention, and inhibitory control: a double-blind, placebo-controlled, crossover study2022A Randomized, Triple-Blind, Placebo-Controlled, Crossover Study to Investigate the Efficacy of a Single Dose of AlphaWave®l-Theanine on Stress in a Healthy Adult Population2021
All 15 studiesEvery publication linked to L-Theanine

Why people take it

Stress & Mood21.1%
Cognition20.7%
Energy13.2%
Sleep12.8%
Essential Health11.1%
Fitness7.1%

SuppCo community snapshot, 2026-09-28. Reasons for use are not evidence that it works.

Questions people ask

Is L-theanine the same as caffeine?

No. They are distinct tea constituents, and studies test them both separately and together. 3

Does it work immediately?

Some attention studies assess effects within the first two hours. That does not establish immediate relief of anxiety or a lasting benefit. 3

Can tea replace a study tablet?

Not as a like-for-like comparison: tea amounts vary with preparation, and the adult trial used 200 mg of isolated theanine. 2 4

Does it lower cortisol?

Not consistently in the cited research. The four-week adult trial found no significant change in blood or saliva cortisol. 2

Is it a treatment for generalized anxiety disorder?

The placebo-controlled add-on trial did not find an anxiety benefit in people already taking antidepressants. 5

Is long-term daily use established as safe?

A four-week trial cannot establish safety over years; the BfR assessment also did not establish a safe daily amount for isolated theanine. 1 2

Sources