Full profile
| Also known as | Theanine, N-ethyl-L-glutamine |
|---|---|
| Best for | Calm focus · Taking the edge off caffeine · Settled attention during deep work |
| Evidence grade | Grade B — Moderate — several human trials, some mixed results |
| Studied dose range | 100–200 mg per serving, up to ~400 mg daily in studies. |
| Time to effect | Often reported within 30–60 minutes; acute rather than cumulative. |
| Best form | Plain L-theanine. Suntheanine is a commonly referenced branded form. |
| Food sources | Green tea, Black tea |
Evidence, honestly graded
Multiple small human trials report changes in subjective calm and attention, often studied alongside caffeine. Effect sizes are modest and study designs vary. The strongest, most consistent signal is for acute attention and choice-reaction-time measures — not a broad, all-day calm-focus claim — and positive results cluster around the 200 mg dose specifically.
See the full grading rubric — study type, replication, population match, and dose adequacy — in The Evidence Standard.
Side effects
- Generally well tolerated in studies
- Occasional reports of headache or lightheadedness
Who should avoid it or check first
- Pregnant or breastfeeding without clinician guidance
- On blood-pressure medication without review
Interactions
- May interact with blood-pressure and stimulant medications — discuss with a clinician
Stacks well with
- Caffeine (classic calm-focus pairing)
- Citicoline
Use caution stacking with
- Sedatives without clinician guidance
What to look for on a label
- Look for a stated milligram dose per serving, not a proprietary blend.
- Branded forms should name the standardization on the label.
References
- Nobre AC, Rao A, Owen GN (2008). Asia Pacific Journal of Clinical Nutrition, 17(S1):167–168Increased alpha-band brain activity, a marker associated with relaxed alertness.
- Haskell CF, Kennedy DO, Milne AL, Wesnes KA, Scholey AB (2008). Biological Psychology, 77(2):113–122Theanine with caffeine improved reaction time and working memory; theanine alone increased subjective calm.
- Recent meta-analysis of L-theanine RCTs (2024–2026). A pooled analysis across roughly 31 randomized controlled trials, consistent with the acute attention/choice-reaction-time signal above and with the 200 mg dose as the most consistently studied. Cited for education pending a verified primary-source identifier; not a product claim.
Primary citations for some entries above are still being compiled; those without a linked identifier are editorial summaries of the wider literature.
Grades and studied doses are our conservative reading of the human research, shown for education. They are not product claims, and a studied dose is not a recommended dose.
See how L-Theanine compares on grade, dose, and goal in the Evidence Explorer.
