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Amino Acids & Proteins

L-Theanine

Also known as: Theanine, Gamma-glutamylethylamide

The calming amino acid in green tea — promotes relaxed focus without drowsiness, especially paired with caffeine.

  • By IngredientWiki Editorial Team
  • Fact-checked by IngredientWiki Editorial Team
  • Updated 2026-09-26
  • 2 min read

In short

L-theanine is an amino acid found almost exclusively in tea leaves, responsible for the calm alertness people describe after drinking green tea. It crosses the blood-brain barrier and appears to boost relaxing brain waves (alpha activity) and modestly buffer the jitteriness of caffeine. Evidence supports mild stress and anxiety reduction and improved focus when combined with caffeine — with an excellent safety record.

  • Amino acid found in tea leaves, especially green tea
  • Promotes calm alertness rather than sedation
  • Common studied doses: 100–400 mg
  • Famous pairing: 100–200 mg with caffeine for smoother focus

What is L-Theanine?

L-theanine was discovered in green tea in 1949 and explains a paradox of tea culture: a caffeinated drink that feels calming. Structurally similar to the neurotransmitter glutamate, theanine modulates its activity, increases GABA and serotonin, and shifts brain activity toward relaxed alpha waves within about 30–40 minutes. It is not a sedative — most people describe the effect as quiet focus rather than sleepiness, which is why it appears in both sleep supplements and nootropic stacks.

Where it comes from

Natural sources

  • Tea leaves (Camellia sinensis) — green, black, white
  • Small amounts in some mushrooms
  • Traditional tea consumption delivers roughly 10–30 mg per cup

How it's made

Supplemental theanine is produced by fermentation of glutamine derivatives, often branded as Suntheanine.

What it does in products

  • Promotes alpha brain waves (relaxed alertness)
  • Modulates glutamate and increases GABA and serotonin
  • Buffers the stimulant side effects of caffeine
  • Supports sleep quality indirectly via relaxation

Benefits

Stress and anxiety reduction

moderate evidence

Randomized trials show 200–400 mg acutely reduces subjective stress and anxiety in stressful situations, with small-to-moderate effect sizes in pooled analyses.

Focus with caffeine

moderate evidence

The classic 'smart combo': studies combining 100–200 mg theanine with 50–75 mg caffeine find faster, more accurate attention than caffeine alone, with less jitter.

Sleep quality

moderate evidence

As part of sleep blends, 200 mg improves sleep satisfaction in some trials — not by sedation, but by calming the pre-sleep mind, particularly in people with stress-related wakefulness.

Blood pressure in stressful moments

emerging evidence

A few trials show theanine blunts stress-induced blood-pressure spikes — a niche but interesting benefit.

Side effects & safety

Mild drowsiness at high doses (rare)Some people feel a lightheaded calm; lowering the dose or taking it in the evening solves it.
Stomach upset on an empty stomach (rare)Rare; taking with food or tea eliminates it.

Safety considerations

  • Theanine is generally considered safe in pregnancy at supplement doses, but data are limited — consult your provider.
  • May add to the sedating effects of sleep medications or alcohol.
  • Can reduce the stimulant effects of caffeine (usually the desired pairing).
  • Not for: None established; caution when combining with high-dose sedatives

How it's used

In supplements

For stress: 200–400 mg as needed or daily. With caffeine: 100–200 mg theanine per 50–100 mg caffeine (roughly a 2:1 theanine-to-caffeine ratio). For evening relaxation: 200 mg, 30–60 minutes before bed.

Regulatory status

  • Dietary supplement under DSHEA. Theanine has GRAS status for use in foods and beverages.
  • GRAS (generally recognized as safe) for food use.

Popular products containing L-Theanine

  • L-Theanine 200 mg — Double-strength capsulesNOW Foods · Supplement
  • TheanineThorne · Supplement
  • Suntheanine L-TheanineNutricost · Supplement

Product names and brands are shown for reference and belong to their respective owners.

Why the caffeine pairing works

Caffeine blocks adenosine to keep you alert; theanine smooths the resulting spike in arousal by raising inhibitory GABA and calming brain-wave activity. Imaging and EEG studies show the combination increases attention-network efficiency beyond either compound alone. This is, in effect, the pharmacology of a good cup of tea — concentrated into a pill.

Frequently asked questions

Does L-theanine make you sleepy?

Usually not — it promotes relaxation without sedation, and most people remain functional. It can deepen sleep when taken before bed, but daytime doses rarely cause drowsiness at 100–200 mg.

Can I take L-theanine every day?

Yes. Trials use daily dosing for weeks, and no tolerance or withdrawal has been reported. Long tea-drinking cultures amount to a centuries-long natural experiment in safety.

When should I take L-theanine?

Morning or early afternoon with caffeine for focus; evening for relaxation and sleep support. Effects start within 30–40 minutes and last a few hours.

The bottom line

L-theanine is the rare supplement that is both gentle and evidence-backed: modest stress relief, smoother caffeine, and better pre-sleep calm. Expect subtle effects — a quieter mind rather than a dramatic shift.

References

  1. L-theanine compound summary. PubChem (National Library of Medicine). https://pubchem.ncbi.nlm.nih.gov/compound/439378
  2. L-theanine and stress — literature search. PubMed (National Library of Medicine). https://pubmed.ncbi.nlm.nih.gov/?term=L-theanine+stress+randomized
  3. Theanine and caffeine on cognition and mood. Nutritional Neuroscience (PubMed). https://pubmed.ncbi.nlm.nih.gov/18681988/
  4. L-theanine safety and pharmacological profile (review). PubMed (National Library of Medicine). https://pubmed.ncbi.nlm.nih.gov/?term=L-theanine+pharmacology+review