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Also known as Theanine, L-gamma-glutamylethylamide
Amino acid from tea leaves that crosses the blood-brain barrier and increases alpha-wave brain activity; promotes calm alertness without sedation, often paired with caffeine.
We link to relevant studies and leave interpretation to you and your healthcare professional.
Number of audited published findings for L-Theanine by condition. Drill into a pair page for the full breakdown.
Where people report using it and what trials suggest
Common claims the trials do not support
Amino acid from tea that promotes calm alertness; best evidence is for attention/relaxation, typically paired with caffeine.
Safety notes: Very well tolerated. No established upper limit.
Evidence grades reflect study quality and consistency, not marketing claims.
Summaries of published trial results for this compound, grouped by condition. Numbers are reported exactly as the researchers published them — we never calculate or convert.
How to read this table
In short: benefit is what was observed; evidence is how much you should trust the observation. A “Benefit seen” tag on a weak study counts for far less than the same tag on a meta-analysis.
| Outcome measured | What trials found | Effect size | People studied | Duration | Type of evidence | Study |
|---|---|---|---|---|---|---|
| reduction of stress and anxiety | L-theanine at 200-400 mg/day may reduce stress and anxiety compared to control in people exposed to stressful conditions.Benefit seen | 200-400 mg/day | — | — | Systematic review · 2020 | PMID 31758301 |
| brain function (e.g. activation of working memory) | Green tea activated working memory compared to separate administration of caffeine or l-theanine, but no specific numbers were reported.Benefit seen | no number reported | — | — | Systematic review · 2017 | PMID 28899506 |
| cognition (e.g. benefits in memory and attention) |
Associated conditions and community-reported outcomes, wrapped together on one page. Aggregates appear only once enough reports arrive.
How this compound is sold in the UK, and where our readers typically find it.
Retailer search links — we may earn commission on purchases at no cost to you. Commission never affects our evidence ratings.
| Green tea improved memory and attention compared to separate administration of caffeine or l-theanine, but no specific numbers were reported.Benefit seen |
| no number reported |
| — |
| — |
| Systematic review · 2017 |
| PMID 28899506 |
| psychopathological symptoms (e.g. reduction of anxiety) | Green tea reduced anxiety compared to separate administration of caffeine or l-theanine, but no specific numbers were reported.Benefit seen | no number reported | — | — | Systematic review · 2017 | PMID 28899506 |
| Executive function | Executive function scores improved after four weeks of L-theanine vs placebo in 30 people (p=0.031). (p = 0.031)Benefit seen | no number reported | 30 | four weeks | RCT · 2019 | PMID 31623400 |
| Letter fluency (lower half subgroup) | Letter fluency increased in lower-performing individuals after four weeks of L-theanine vs placebo (p=0.002). (p = 0.002)Benefit seen | no number reported | 30 | four weeks | RCT · 2019 | PMID 31623400 |
| Pittsburgh Sleep Quality Index | Sleep quality scores decreased after four weeks of L-theanine vs placebo in 30 people (p=0.013). (p = 0.013)Benefit seen | no number reported | 30 | four weeks | RCT · 2019 | PMID 31623400 |
| PSQI subscale: sleep latency, sleep disturbance, use of sleep medication | Sleep latency, disturbance, and medication use reduced after four weeks of L-theanine vs placebo in 30 people (p<0.05). (all p < 0.05)Benefit seen | no number reported | 30 | four weeks | RCT · 2019 | PMID 31623400 |
| Self-rating Depression Scale | Depression scores decreased after four weeks of L-theanine vs placebo in 30 people (p=0.019). (p = 0.019)Benefit seen | no number reported | 30 | four weeks | RCT · 2019 | PMID 31623400 |
| State-Trait Anxiety Inventory-trait | Anxiety scores decreased after four weeks of L-theanine vs placebo in 30 people (p=0.006). (p = 0.006)Benefit seen | no number reported | 30 | four weeks | RCT · 2019 | PMID 31623400 |
| Verbal fluency | Verbal fluency scores improved after four weeks of L-theanine vs placebo in 30 people (p=0.001). (p = 0.001)Benefit seen | no number reported | 30 | four weeks | RCT · 2019 | PMID 31623400 |
| Verbal fluency (lower half subgroup) | Verbal fluency increased in lower-performing individuals after four weeks of L-theanine vs placebo (p=0.002). (p = 0.002)Benefit seen | no number reported | 30 | four weeks | RCT · 2019 | PMID 31623400 |