Herb record · Theaceae
L-theanine (green tea) tea: what the evidence says
Reviewed
The amino acid behind green tea's 'calm focus' reputation. Trials use 200–400 mg supplements; green tea itself also contains caffeine.
At a glance
- Latin name
- from Camellia sinensis
- Evidence
- Extract trials only Human trials exist, but they used extracts, capsules or supplements, not tea.
- EU tea amount
- The EU monographs we use list no tea preparation for this herb.
- Cautions
- Contains caffeineWarfarin interaction reported
- In our index
- No teas yet
What did the studies actually test?
Each row says what form was given. Results from extracts or capsules don't automatically apply to a cup of tea, which usually contains a smaller and less standardized amount.
| Question | Form tested | What was found |
|---|---|---|
| Stress & anxiety | supplement | Trials of 200–400 mg/day L-theanine supplements suggest less stress and anxiety in people under stressful conditions. (Williams et al., 2020)(Hidese et al., 2019) |
| Sleep | supplement | A 2025 meta-analysis of supplement trials found small improvements in self-reported time to fall asleep and sleep quality. (Bulman et al., 2025) |
| Tea form | tea | These trials gave L-theanine on its own. A cup of green tea also contains caffeine, so the tea isn't equivalent to the supplement. (NCCIH fact sheet) |
Who should be careful with l-theanine (green tea)?
- Contains caffeine. Green tea contains caffeine. High doses reduced blood levels of the beta-blocker nadolol, and other drug interactions are possible. (NCCIH fact sheet)
- Warfarin interaction reported. Green tea is among items reported to raise bleeding risk with warfarin. (Tan & Lee, 2021)
This list repeats what the cited sources say; it isn't a complete interaction check. A pharmacist can check your specific medicines.
Which calming teas contain l-theanine (green tea)?
None of the Calm Teas index teas list it. Browse the tea decoder.
Sources
- Williams et al. (2020). The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review. Plant Foods Hum Nutr.
Systematic review · form: supplement
9 randomized trials of L-theanine supplements. 200–400 mg/day may help reduce stress and anxiety in people under stressful conditions.
Limits: Supplement doses; authors call for longer, larger trials including dietary intake.
checked against the abstract, 2026-10-21 · PMID 31758301 - Hidese et al. (2019). Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients.
Human trial (randomized, double-blind, placebo, crossover) · form: supplement
30 healthy adults took 200 mg/day L-theanine or placebo for 4 weeks. Depression, trait anxiety and sleep-quality scores decreased after L-theanine.
Limits: Small; tablets, not tea.
checked against the abstract, 2026-10-21 · PMID 31623400 - Bulman et al. (2025). The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis. Sleep Med Rev.
Systematic review + meta-analysis · form: supplement
19 articles (897 participants) on L-theanine supplements. Small improvements in subjective time to fall asleep, daytime dysfunction and overall sleep-quality scores.
Limits: Supplement doses, not tea; authors note few studies of pure L-theanine.
checked against the abstract, 2026-10-21 · PMID 40056718 - NCCIH (NIH). Green Tea, updated February 2025.
Government fact sheet
No safety concerns reported for green tea as a beverage in adults, but it contains caffeine. High doses reduced levels of the beta-blocker nadolol; interactions with other drugs possible.
checked against the official page, 2026-10-21 - Tan & Lee (2021). Warfarin and food, herbal or dietary supplement interactions: A systematic review. Br J Clin Pharmacol.
Systematic review (interactions) · form: mixed
78 foods, herbs and supplements reported to interact with warfarin. Chamomile tea and green tea are among those the authors list as raising bleeding risk.
Limits: Much of the underlying evidence is case reports.
checked against the abstract, 2026-10-21 · PMID 32478963