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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

Can it take the edge off stress?

A systematic review of nine articles found a promising signal for 200–400 mg daily in people facing stressful situations. The authors called for larger and longer trials before treating this as an established therapy. 1

StressToo little evidence

The evidence supports further study of situational stress relief. It does not establish that everyone will feel calmer or identify a reliable long-term regimen. 1

What about an anxiety disorder?

In a placebo-controlled trial of 46 people with generalized anxiety disorder who were already taking antidepressants, additional theanine did not improve the main anxiety outcome. Overall insomnia severity also did not improve, although one sleep-satisfaction item favored theanine. 2

AnxietyNot supported

This trial does not support theanine as an effective add-on treatment for generalized anxiety disorder. Its sleep finding is a separate, narrower question. 2

Does it improve sleep?

A 2025 meta-analysis found improvements in self-reported sleep quality, time to fall asleep and daytime functioning. A central limitation was the shortage of studies testing pure theanine: results from combination products cannot reveal which ingredient helped. 3

Sleep qualityMixed

There is a useful sleep signal, but the best dose and duration remain unsettled. These findings are not yet a dependable treatment plan for persistent insomnia. 3

Theanine alone or with caffeine?

A 2025 review of 50 randomized trials found some short-term attention benefits from theanine with caffeine and a faster choice-reaction response with theanine alone. Results varied across tasks, and several estimates remained compatible with no benefit. The authors disclosed tea-industry funding or employment relationships. 4

Focus And AttentionMixed

Laboratory attention tasks offer a promising lead, but they do not establish better everyday productivity. A result for the combination cannot be assigned entirely to theanine. 4

Feeling better is not the same as lowering cortisol

A crossover trial in 30 adults used 200 mg daily for four weeks. Some sleep subscales improved compared with placebo, but blood and saliva cortisol did not change significantly. This helps separate a possible symptom benefit from claims that theanine consistently lowers the stress hormone. 5

Effects by health goal

Open an effect to see the studies behind its rating. Bars show the size of the effect; the letter grades the evidence.

Stress & Mood4 effects

StressStress & MoodModerateA3 studies
Safety and Efficacy of AlphaWave® l-Theanine Supplementation for 28 Days in Healthy Adults with Moderate Stress: A Randomized, Double-Blind, Placebo-Controlled Trial2024Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial2019l-Theanine reduces psychological and physiological stress responses2007

Rated by SuppCo · high confidenceEvidence record

Mood SupportStress & MoodModerateBNo linked study

No study is linked to this rating.

Rated by SuppCo · medium confidenceEvidence record

AnxietyStress & MoodModerateB3 studies
The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review2019Psychotropic effects of L-theanine and its clinical properties: from the management of anxiety and stress to a potential use in schizophrenia.2019l-Theanine reduces psychological and physiological stress responses2007

Rated by SuppCo · medium confidenceEvidence record

Cortisol stressStress & MoodSmallB3 studies
Safety and Efficacy of AlphaWave® l-Theanine Supplementation for 28 Days in Healthy Adults with Moderate Stress: A Randomized, Double-Blind, Placebo-Controlled Trial2024A 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 Population2021Serum Levels of Brain-Derived Neurotrophic Factor and Cortisol to Sulfate of Dehydroepiandrosterone Molar Ratio Associated With Clinical Response to l-Theanine as Augmentation of Antipsychotic Therapy in Schizophrenia and Schizoaffective Disorder Patients2011

Rated by SuppCo · medium confidenceEvidence record

All studies

15 publications are linked to L-Theanine, newest first.

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 Population2021L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover study2020Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial2019The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review2019Psychotropic effects of L-theanine and its clinical properties: from the management of anxiety and stress to a potential use in schizophrenia.2019Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis.2014Serum Levels of Brain-Derived Neurotrophic Factor and Cortisol to Sulfate of Dehydroepiandrosterone Molar Ratio Associated With Clinical Response to l-Theanine as Augmentation of Antipsychotic Therapy in Schizophrenia and Schizoaffective Disorder Patients2011Effects of L-theanine on attention and reaction time response2011The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness2010L-theanine, a natural constituent in tea, and its effect on mental state.2008l-Theanine reduces psychological and physiological stress responses2007

Sources