L-theanine

Also known as: Theanine, Suntheanine

An amino acid found in tea leaves, often paired with caffeine to smooth out its effects.

Common forms: Capsules · Powder · Green tea

Draft summary, not yet reviewed by a qualified health professional · Last updated 2026-11-03

Talk to a healthcare professional first

This information is for education only and is not medical advice, diagnosis, or treatment. Supplements can interact with medications and health conditions. Check with your doctor or pharmacist before starting anything, especially if you take medication, are pregnant or breastfeeding, or have a health condition. These statements have not been evaluated by the FDA; supplements are not intended to diagnose, treat, cure, or prevent any disease.

What the evidence says

Focus & alertness

BModerate evidence

A 2026 meta-analysis of 31 trials found a single 200 mg dose improved reaction time and attention in healthy adults. Combinations with caffeine have also shown benefits for attention.

Dose used in studies: 200 mg, 30–60 minutes before the task (optionally with 50–100 mg caffeine)
Time to effect: 30–60 minutes

Studies (2)

Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis — Nutr Rev, 2014 · Meta-analysis · PMID 24946991
Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of Randomized Controlled Trials — Nutr Rev, 2025 · Meta-analysis · PMID 40314930

Stress & anxious feelings

CLimited evidence

Meta-analysis found only a modest reduction in acute stress, largely driven by studies at high risk of bias; effects on anxiety were inconsistent.

Dose used in studies: 200–400 mg/day
Time to effect: Acute to 4 weeks

Studies (2)

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, 2020 · Systematic review · PMID 31758301
Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials — Mol Psychiatry, 2026 · Meta-analysis · PMID 42410082

Safety

Common side effects

Generally well tolerated
Occasional headache or nausea

Pregnancy & breastfeeding

Not enough safety data — avoid unless your provider recommends it.

Medication interactions

minorBlood pressure medications: May slightly lower blood pressure.
minorSedatives / sleep medications: May add to relaxing effects.

This list covers common medication classes only and is not exhaustive.

Buying tips

Look for third-party testing seals (USP Verified, NSF Certified, or Informed Choice) and match the form and dose used in studies.

Where to buy (affiliate)