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Amino acid

L-theanine

amino acid from tea

An amino acid found mainly in tea, studied for calm focus and stress.

Evidence: Limited to moderate

A systematic review of 5 randomized trials (104 participants) concluded that L-theanine may reduce acute stress and anxiety in people in stressful situations. Four of five studies were significant, but the sample sizes were small and one trial compared with a drug showed no effect for either.

At a glance

Typical studied dose
Systematic-review trials used 200-400 mg per day, for up to 8 weeks.

Food sources

Plant sources
Green, black and white tea; very small amounts in some mushrooms.

Background and testing

This is not an essential nutrient, so there is no deficiency to diagnose.

Who tends to use it
Adults looking for support for everyday stress; tea drinkers get small amounts.
How it is tested
No lab test.

Supplement forms

Common forms
Capsules, tablets, powders, tea, and combination products with caffeine.
More effective
L-theanine alone at 200 mg or more, taken at the time of need. Combining with caffeine has been studied for attention.
Less effective
Relying on tea alone for a supplement-level dose (a cup has roughly 20-30 mg); products with unspecified amounts; very high doses without a reason.

Safety, interactions and halal notes

Safety and interactions
Generally well tolerated in short trials. Side effects are uncommon and mild (headache, dizziness). It may add to blood-pressure-lowering or sedative medicines.
Who should avoid it or ask a clinician first
People on blood-pressure or sedative medicines should ask a clinician; pregnant and breastfeeding women (limited data).
Halal note
Typically fermentation- or synthesis-derived and plant-based. Check capsule shells and flavorings.

Frequently asked questions

Does L-theanine make you drowsy?

It is usually described as calming without strong sedation, but responses vary.

Sources

  1. Theanine consumption, stress and anxiety in human clinical trials: a systematic review (2015)

← Back to the full nutrient guide

This page is for education only and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Supplements are not intended to diagnose, treat, cure or prevent any disease. Talk to a qualified clinician before starting a supplement, especially if you are pregnant, breastfeeding, take medicine or have a medical condition. Daily needs are US reference intakes for adults 19-50.

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