What is the studied dose of L-Theanine?

50–250 mg per serving across the trials cited here (Nobre 50 mg; Haskell 250 mg), most commonly 100–200 mg. A studied dose is what research used, not a recommended dose.

What are the side effects of L-Theanine?

Generally well tolerated in studies Occasional reports of headache or lightheadedness

Who should avoid L-Theanine?

Pregnant or breastfeeding without clinician guidance On blood-pressure medication without review

Amino acid

L-Theanine

An amino acid found in tea leaves. It is studied for promoting a calm, settled kind of attention without sedation, which fits a stimulant-free focus direction.

Grade BSignal State Core candidateUpdated September 17, 2026Written and fact-checked in-house against The Evidence Standard. Not a clinical review.

Photo by Timothy Newman on Unsplash

Please note

Educational content, not medical advice. Doses below are ranges used in research, not recommendations. Talk to a qualified clinician before starting any supplement, especially if you take medication, are pregnant, or manage a health condition.

Evidence grade: Evidence: Grade B
Studied dose range: 50–250 mg per serving across the trials cited here (Nobre 50 mg; Haskell 250 mg), most commonly 100–200 mg.
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.

The short answer

L-Theanine (Amino acid) is studied for calm focus and taking the edge off caffeine. In our conservative reading of the published human research, the evidence is Grade B (moderate). 50–250 mg per serving across the trials cited here (Nobre 50 mg; Haskell 250 mg), most commonly 100–200 mg. Often reported within 30–60 minutes; acute rather than cumulative. A studied dose is what trials used, not a recommended dose.

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	50–250 mg per serving across the trials cited here (Nobre 50 mg; Haskell 250 mg), most commonly 100–200 mg.
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

Held at B on 2026-09-14; with Bacopa, it is one of the two B-graded actives in the Signal State Core concept formula. A 2026 meta-analysis of 31 randomized trials (Gerolymos et al.) found a single 200 mg dose improved attention and reaction-time measures versus placebo (SMD 0.51); its acute-stress effect was smaller and leaned on higher-risk-of-bias studies, and it found no effect on fatigue. A 2025 meta-analysis of sleep trials (Bulman et al.) found better self-rated sleep quality and daytime functioning, but no change on objective sleep measures. What keeps it short of A: the attention signal shows up mainly on reaction-time tasks rather than as a broad, all-day calm-focus effect, most trials are small, several are industry-linked, and a smaller 2025 meta-analysis of five trials in 148 healthy adults (Mátyus et al.) splits: it found a dose-dependent improvement in rapid visual information processing and recognition reaction time (−15.20 ms), but no effect on simple reaction time or Stroop performance. Positive acute trials cluster in the 100–250 mg range; Health Canada's monograph permits a relaxation claim only, at 200–250 mg/day.

See the full grading rubric (study type, replication, population match, and dose adequacy) in The Evidence Standard.

What the benefits research does and doesn't support, in depth: L-Theanine Benefits: What the Research Actually Supports.

1,656 natural health products with an active licence in Health Canada's LNHPD list L-Theanine as a medicinal ingredient.

That makes L-Theanine a recognized, licensable medicinal ingredient in Canada, regulated by Health Canada's Natural and Non-prescription Health Products Directorate, which issues each licensed natural health product a Natural Product Number (NPN). Search the LNHPD to verify.

Source: Health Canada Licensed Natural Health Products Database, snapshot 2026-09-28. A count of products with an active licence, not an endorsement of any health claim. This describes the ingredient's regulatory standing in Canada, not Signal State Core, which is a pre-launch concept and is not a licensed natural health product.

Side effects

Generally well tolerated in studies
Occasional reports of headache or lightheadedness

The full side-effect breakdown: L-Theanine Side Effects: What the Research Actually Shows.

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):167–168Human EEG study, 50 mg single doseStudied dose: 50 mgIncreased 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):113–122Randomized, placebo-controlled, double-blind crossoverStudied dose: 250 mg (with and without 150 mg caffeine)Theanine with caffeine improved reaction time and working memory; theanine alone increased subjective calm.
Gerolymos C, Saddier E, Boyer L, Fond G (2026). Molecular PsychiatrySystematic review and meta-analysis, 31 RCTs, n=1,168Studied dose: 200 mg single doseA single 200 mg dose improved attention and reaction-time measures versus placebo (SMD 0.51, 95% CI 0.25–0.77); the acute-stress effect was smaller and driven by higher-risk-of-bias studies.
Bulman A, D'Cunha NM, Marx W, et al. (2025). Sleep Medicine Reviews, 81Systematic review and meta-analysis, 19 studies (18 pooled), n=897Improved self-rated sleep quality (SMD 0.43), daytime dysfunction (SMD 0.33) and sleep-onset latency (SMD 0.15); no objective sleep measure changed significantly.
Mátyus RO, Szikora Z, Bodó D, et al. (2025). Journal of Clinical Medicine, 14(21):7710Systematic review and meta-analysis, 5 RCTs, n=148 healthy adultsA dose-dependent improvement in rapid visual information processing and recognition visual reaction time (−15.20 ms, 95% CI −28.99 to −1.41); no significant effect on simple reaction time or on the Stroop test.
Payne ER, Aceves-Martins M, Dubost J, et al. (2025). Nutrition Reviews, 83(10):1873–1891Systematic review of 50 RCTs in healthy participants, 15 pooled in meta-analysesTheanine alone favoured over placebo on choice reaction time one hour after intake (SMD −0.35, 95% CI −0.61 to −0.10); theanine plus caffeine showed small-to-moderate gains on several attention measures.

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.

Revision history

Every change to this ingredient's evidence status, dated and explained. The full cross-library log lives at Evidence Updates.

2026-09-17Citation review
Corrected a one-sided description. This profile reported that the 2025 five-trial meta-analysis found no effect on simple reaction time or the Stroop test, which is true but leaves out that the same analysis found a dose-dependent improvement in rapid visual information processing and recognition reaction time. Both findings are now stated and the meta-analysis is cited in full, alongside a larger 2025 tea review whose Lipton and Unilever funding is disclosed. B holds.
2026-09-14Citation review
Held at B with two new meta-analyses added: a 2026 review of 31 RCTs found a single 200 mg dose improved attention and reaction time, and a 2025 review found improvements in self-rated, but not objectively measured, sleep.
2026-07-07New profile
Initial profile published at Grade B: multiple small human trials show acute calm and attention effects, often studied alongside caffeine, with modest and variable effect sizes.

See how L-Theanine compares on grade, dose, and goal in the Evidence Explorer.

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