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.

Evidence: Grade BSignal State Core candidateUpdated 2026-07-26Written and fact-checked in-house against The Evidence Standard — not a clinical review

Fresh green tea leaves in soft light — the natural source of L-theanine — Photo by Timothy Newman on Unsplash

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.

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.

Evidence grade: 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.

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

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 — with positive trials clustering in the 100–250 mg acute-dose range used in the cited studies.

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

1,647 licensed natural health products 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 2026-07-26 — a count of licensed products, 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

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.

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.

2026-07-07New 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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