L-Theanine
Amino acid (found in tea)
Also known as: N-ethyl-L-glutamine
An amino acid from tea leaves used for calm focus and to smooth out caffeine's edge. Well tolerated with moderate supporting evidence.
Several small RCTs support acute stress reduction and attention benefits, especially with caffeine.
Some human RCTs, but limited size, replication, or scope.
Intended use
Used for relaxation, stress reduction, and 'calm alertness', frequently paired with caffeine.
Mechanism of action
Crosses the blood-brain barrier and increases alpha brain-wave activity while modulating GABA, dopamine, and serotonin.
Reported benefits
Calm focus
Increases alpha-wave activity associated with relaxed alertness.
Synergy with caffeine
Improves attention and reduces jitteriness when combined with caffeine.
Stress reduction
Small trials show reduced acute stress markers.
Risks & side effects
Very low risk
low riskGenerally recognized as safe; side effects are rare and mild.
Blood pressure interaction
low riskMay slightly lower blood pressure; caution with hypotensives.
Research & citations
Studies are ordered by design strength. Dots indicate the rigor of each study type — meta-analyses and double-blind RCTs rank highest, case reports and in vitro work lowest.
- L-theanine effects on stress and cognition
Acute reduction in stress/anxiety under stressful conditions.
Plant Foods for Human Nutrition · 2020 · n = Multiple RCTs
Meta-analysis / Systematic review - L-theanine and caffeine on attention and mood
Improved attention-switching accuracy and alertness.
Nutritional Neuroscience · 2008 · n = ~27
Double-blind RCT
Legal status by region
Regulatory status varies widely and changes often. Verify against current local law before acting.
| Region | Status | Notes |
|---|---|---|
| United States | Over the counter | Legal dietary supplement (GRAS). |
| European Union | Over the counter | Sold as a food supplement. |
| United Kingdom | Over the counter | Available as a supplement. |
| Australia | Over the counter | Available as a complementary medicine. |
Sourcing & prescribing
Where a compound can legally be obtained, and who is able to prescribe it.
- Legal
Retail supplement stores
Widely available OTC.
- Legal
Green/black tea
Naturally present in tea.
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