L-theanine
Summary
A single 200 mg serving of L-theanine improved reaction time on attention tests in pooled trials. Effects on acute stress were modest and came largely from studies at high risk of bias, and anxiety results were inconsistent. Small 4-week trials reported better sleep and stress scores. No serious adverse events were reported across 31 trials.
Key facts
- L-theanine capsules or tablets (including branded forms), L-theanine combined with caffeine, and tea[1][2][4]
- Theanine plus caffeine gave small-to-moderate gains in attention and mood in the first 2 hours versus placebo; theanine alone also improved choice reaction time (meta-analysis)[2]
- Attention (choice reaction time) ↑ (B); acute stress ↓ modest, high risk of bias (C); stress and sleep scores over 4 weeks: mixed small trials (D)[1][3][4]
- No serious adverse events were reported across 31 randomized trials (n=1,168)[1]
- 4 graded human outcomes on this page
- October 9, 2026
How it works
ProposedHow L-theanine might affect attention and stress is not established in our sources. It occurs in tea with caffeine, and trials test it alone and in combination, where it appears to add to caffeine's effects on attention (proposed).[2]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Focus | Grade B | Improved | Meta-analysis · n = 1,168 · 2026 | 2 rows |
| Stress | Grade D | Improved | Crossover RCT · n = 30 · 2019 | 2 rows |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Attention (choice reaction time) and acute stress | Improved | Grade B | Meta-analysis · n = 1,168 · 2026 Healthy and clinical populations in 31 randomized placebo-controlled trials Form: L-theanine (oral) · Dose: 200 mg single dose 30–60 minutes before testing; 400 mg/day for 8 weeks in one trial · Duration: Single doses and repeated dosing A single 200 mg dose improved choice reaction time (SMD 0.51). Acute stress fell modestly (SMD 0.31), mostly driven by studies at high risk of bias; fatigue did not change, and anxiety effects were inconsistent. No serious adverse events were reported. | 42410082 (opens PubMed)Source [1] |
| Attention and alertness with caffeine | Improved | Grade D | RCT · n = 44 · 2010 Young adults Form: L-theanine plus caffeine vs placebo · Dose: 97 mg L-theanine with 40 mg caffeine · Duration: Single dose; tested at 20 and 70 minutes The combination improved accuracy during task switching and self-reported alertness, and reduced tiredness. Visual search, choice reaction time and mental rotation did not change. | 21040626 (opens PubMed)Source [5] |
| Stress, sleep quality and cognition over 4 weeks | Improved | Grade D | Crossover RCT · n = 30 · 2019 Healthy adults (9 men, 21 women; mean age 48) without major psychiatric illness Form: L-theanine tablets vs placebo · Dose: 200 mg/day · Duration: 4 weeks per period Depression, trait-anxiety and sleep-quality (PSQI) scores decreased after L-theanine; sleep latency, sleep disturbance and use of sleep medication subscales fell compared with placebo. Verbal fluency and executive function scores improved. | 31623400 (opens PubMed)Source [3] |
| Perceived stress and sleep in adults with moderate stress | Mixed | Grade D | RCT · n = 30 · 2024 Healthy adults aged 18–65 with moderate stress (15 per group) Form: branded L-theanine (AlphaWave) vs placebo · Dose: 400 mg/day · Duration: 28 days Perceived stress fell by about 18% with both L-theanine and placebo, and salivary cortisol did not differ between groups. L-theanine reduced light sleep versus placebo but also decreased time asleep at 28 days, and improved Stroop reaction time earlier than placebo. | 38758503 (opens PubMed)Source [4] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| L-theanine capsules or tablets | 100%[1] | No head-to-head absorption data in our sources. A single 200 mg dose improved choice reaction time.[1] | No serious adverse events were reported in the trials pooled.[1] | Attention, stress, sleep |
| L-theanine with caffeine | Varies[5] | Small-to-moderate gains in attention and mood in the first 2 hours versus placebo (meta-analysis).[2] | Products also carry caffeine's side effects; no combination-specific tolerance data in our sources.[2] | Attention and alertness |
| Tea (green or black) | Varies[2] | Few trials used tea-equivalent doses; authors call for more research with tea beverages.[2] | No form-specific tolerance data in our sources.[2] | Cognition, mood and sleep in healthy people |
Compound weight → elemental active
500 mg l-theanine capsules or tablets ≈ 500 mg elemental active
Studied doses
Doses studied in human trials ranged from about 100 mg (with caffeine) to 400 mg of L-theanine a day, from single servings 30 to 60 minutes before testing up to 8 weeks.[1][3][4][5]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Who should be careful
- Limited safety data
- No serious adverse events were reported across 31 randomized trials, but most were short. Data on pregnancy, breastfeeding and long-term use were not reported in our sources.[1]
- Combination products
- Many products pair theanine with caffeine; check the caffeine content.[2]
- Before you start
- Talk to your pharmacist or clinician before adding this supplement, especially if you take prescription medicines, are pregnant or breastfeeding, or have a chronic health condition.[1]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Cost per studied dose, without the sales pitch
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Cost per studied dose
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Articles about L-theanine
Plain-English answers to common questions, built on the evidence above.
Frequently asked questions
Does L-theanine improve focus?
In a 2026 meta-analysis of 31 trials, a single 200 mg dose taken 30–60 minutes before testing improved choice reaction time, a measure of attention.[1]
Does L-theanine reduce stress or anxiety?
The effect on acute stress was modest and mainly came from studies at high risk of bias, and anxiety results were inconsistent. In one 28-day trial, perceived stress fell just as much with placebo.[1][4]
Does L-theanine help sleep?
Evidence is limited to small trials. In a 4-week crossover trial of 30 adults, 200 mg/day improved sleep-quality scores, and a 28-day trial found less light sleep than placebo.[3][4]
Why is L-theanine paired with caffeine?
Both occur in tea. Pooled trials found the combination improved attention and mood measures in the first 2 hours, and one trial of 97 mg theanine with 40 mg caffeine improved task-switching accuracy and alertness.[2][5]
Is L-theanine safe?
No serious adverse events were reported across 31 randomized trials, though most were short-term.[1]
Sources
- [1]Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials.. Mol Psychiatry, 2026. meta-analysis
- [2]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
- [3]Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial.. Nutrients, 2019. crossover-RCT
- [4]Safety and Efficacy of AlphaWave® L-Theanine Supplementation for 28 Days in Healthy Adults with Moderate Stress: A Randomized, Double-Blind, Placebo-Controlled Trial.. Neurol Ther, 2024. RCT
- [5]The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness.. Nutr Neurosci, 2010. RCT
What changed
- First draft. Every evidence-row PMID checked with NCBI E-utilities (esummary + efetch abstract) and re-read in an independent adversarial pass.
- Added cost-per-studied-dose method, labeled analysis derived from cited rows.