Healthy-adult stress and sleep studies used 200 mg/day or 200 mg before bed for 4–8 weeks
Reviewed · Published
L-theanine
A tea amino acid studied for relaxation without marked sedation.
Established functions
- A tea amino acid studied for relaxation without marked sedation.
Dietary sources
- green tea
- gyokuro tea
Claims and evidence
Claims that L-theanine alone prevents or treats disease, or invariably improves health without deficiency, are unsupported.
Japanese reference amounts
- Japanese adults (age and sex as specified): No Japanese DRI established
Amounts studied
- Healthy-adult stress and sleep studies used 200 mg/day or 200 mg before bed for 4–8 weeks
Tolerable upper limits
- No UL; long-term ceiling unknown
Forms and bioavailability
Supplement forms: tea-extracted L-theanine, fermentation-derived L-theanine
- Check residual caffeine in tea extracts and purity of fermentation products.
Safety and interactions
Adverse effects
- headache
- drowsiness
- gastrointestinal effects
- lower blood pressure
Medicine and nutrient interactions
- antihypertensives, sedatives, caffeine
Contraindications and cautions
- Consult before use with low blood pressure, pregnancy, or lactation.
Practical selection
- Compare L-theanine amount per serving, form, allergens, and batch testing; prefer a single-ingredient product suited to the intended use.
Sources and review
- NCCIH Herbs at a Glance and supplement safety resourcesNational Center for Complementary and Integrative Health
Daiki Minaki (editorial and evidence review) ·
Frequently asked questions
How is L-theanine different from its broader supplement category?
A tea amino acid studied for relaxation without marked sedation. Compare its named form and amount rather than assuming every category product supplies it.
View detailsWhat safety detail matters specifically for L-theanine?
antihypertensives, sedatives, caffeine Consult before use with low blood pressure, pregnancy, or lactation.
View details