L-Theanine
Also called Theanine, Suntheanine, N-ethyl-L-glutamine
L-theanine is an amino acid found in tea leaves. Research has addressed several effects: alpha brain-wave activity, anxiety reduction without sedation, and its combined effect with caffeine.
- Evidence
- AStrong evidence
- Studied dose
- 100-400mg
- Safety score
- Verified references
- 5 studies
How it is thought to work
Where to buy L-Theanine
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| Vendor | Product | Size | Price | Per unit | Buy |
|---|---|---|---|---|---|
| Amazon |  Nutricost L-Theanine 200mg, 120 Capsules, Double Strength... | - | On Amazon | - | Check price on Amazon Ad |
| NOW Foods |  NOW Foods L-Theanine, Double Strength 200 mg Per Cap - 180... | - | On Amazon | - | Check price on Amazon Ad |
| iHerb | Nutricost, L-Theanine, 200 mg, 30 Capsules | - | about $8.76 at iHerb (as of 24 September 2026) | - | Shop Ad |
| iHerb | NOW Foods, L-Theanine, 120 Veg Capsules | - | about $20.79 at iHerb (as of 24 September 2026) | - | Shop Ad |
| iHerb | Sports Research, L-Theanine, 200 mg, 60 Softgels | - | about $20.97 at iHerb (as of 24 September 2026) | - | Shop Ad |
What the studies found
| Claimed benefit | Grade | Basis |
|---|---|---|
| Alpha brain wave activity / relaxed focus | A | Nobre 2008.[2] |
| Anxiety reduction without sedation | A | Kimura 2007.[1] |
| Synergy with caffeine | A | Owen 2008.[3] |
Each benefit is graded on its own; a substance can have strong evidence for one effect and little for another. What the grades mean.
All three graded benefits are rated A. Increased alpha brain-wave activity, associated with relaxed alertness, rests on Nobre 2008[2]. Reduced psychological and physiological stress responses rest on Kimura 2007[1]. Effects of the caffeine combination on cognitive performance and mood rest on Owen 2008[3], with a related trial by Haskell 2008[4].
Dose and timing
Doses used in the research on file, taken as 1-2 doses. Not a recommendation.
Logarithmic time scale. Individual metabolism varies.
Safety and interactions
| Recorded side effect | How often | Severity |
|---|---|---|
| Very few reported | rare | mild |
The interaction records list no combination rated caution or avoid.
Side effects in detailRecorded interactionsInteraction checker
History
References
- L-Theanine reduces psychological and physiological stress responses (Kimura). 2007. PubMed 16930802
- L-theanine, a natural constituent in tea, and its effect on mental state (Nobre). 2008. PubMed 18296328
- The combined effects of L-theanine and caffeine on cognitive performance and mood (Owen). 2008. PubMed 18681988
- The effects of L-theanine, caffeine and their combination on cognition and mood (Haskell). 2008. PubMed 18006208
- The neuropharmacology of L-theanine (N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent (Nathan). 2006. PubMed 17182482
Reader reviews
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Sign in to reviewL-Theanine: quick answers
- How strong is the evidence for L-Theanine?
- The overall grade on file is A (strong). 3 claimed benefits are graded separately in the table above. The entry cites 5 studies.
- What dose of L-Theanine has been studied?
- The range on file is 100-400 mg (1-2 doses). It describes doses used in research, not a recommendation.
- How long does L-Theanine take to work and how long does it last?
- Listed onset: about 30 minutes. Listed half-life: about 1 hour. Individual metabolism varies.
- What are the side effects of L-Theanine?
- Recorded side effects: Very few reported (rare). Safety score 5/5.
Compared with other substances
Show 24Hide
| Comparison | Grade | Class |
|---|---|---|
| L-Theanine vs Caffeine | A | Stimulant |
| L-Theanine vs Ashwagandha | A | Adaptogen |
| L-Theanine vs Magnesium L-Threonate | B | Neuroprotective |
| L-Theanine vs Apigenin | B | Neuroprotective |
| L-Theanine vs Creatine | A | Amino acid |
| L-Theanine vs 5-HTP | B | Amino acid |
| L-Theanine vs Agmatine Sulfate | B | Amino acid |
| L-Theanine vs Beta-Alanine | A | Amino acid |
| L-Theanine vs Carnosine | C | Amino acid |
| L-Theanine vs Dihydromyricetin (DHM) | B | Amino acid |
| L-Theanine vs GABA | C | Amino acid |
| L-Theanine vs Glycine | B | Amino acid |
| L-Theanine vs L-Arginine | B | Amino acid |
| L-Theanine vs L-Carnitine | A | Amino acid |
| L-Theanine vs L-Citrulline | A | Amino acid |
| L-Theanine vs L-Glutamine | B | Amino acid |
| L-Theanine vs L-Tryptophan | B | Amino acid |
| L-Theanine vs L-Tyrosine | A | Amino acid |
| L-Theanine vs N-Acetyl Cysteine (NAC) | B | Amino acid |
| L-Theanine vs N-Acetyl L-Tyrosine (NALT) | C | Amino acid |
| L-Theanine vs PEA (Phenylethylamine) | C | Amino acid |
| L-Theanine vs Pantogam (Hopantenic Acid) | C | Amino acid |
| L-Theanine vs Picamilon | C | Amino acid |
| L-Theanine vs Taurine | B | Amino acid |
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