L-Theanine
Green-tea amino acid for calm, focused alertness.
Evidence tier
Moderate
Research weight
Citations
16 verified / 16
Classification
Nootropic
❝
What the evidence says. Several controlled trials; effects real but modest or context-dependent.
What is L-Theanine?
L-Theanine is a nootropic used for calm focus. NutriDex grades the human evidence as Moderate. L-theanine is an amino acid found in tea that increases alpha brain-wave activity associated with relaxed alertness. Trials show reduced stress reactivity and anxiety, and — combined with caffeine — improved attention and reaction time while blunting caffeine's jittery edge. Effects on sleep architecture are modest but it can improve subjective relaxation before bed without sedation.
Purported Benefits
✓Calm focus
✓Reduced anxiety
✓Better sleep quality
✓Smooths caffeine jitters
Evidence by outcome
The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.
| Outcome | Evidence | Effect | Studies |
|---|---|---|---|
| Stress & anxiety reductionSystematic reviews of RCTs show 200-400 mg/day reduces stress/anxiety under stressful conditions; small samples. | Moderate | ↑ benefit · small | 3 |
| Calm focus / attention with caffeineMeta-analysis of 50 RCTs shows small-moderate first-2-hour gains in attention-switching and alertness when combined with caffeine. | Moderate | ↑ benefit · small | 3 |
| Sleep qualityMeta-analysis of 18 RCTs found improved subjective sleep quality (SMD 0.43) and onset latency without sedation. | Moderate | ↑ benefit · small | 3 |
| Standalone cognition / reaction timeDose-dependent gains in visual processing/reaction time but no consistent effect across other cognitive tests. | Preliminary | ↔ mixed · small | 2 |
| Psychiatric symptom adjunct (schizophrenia/anxiety/ADHD)Systematic review of 11 RCTs reports symptom reduction across disorders but calls for larger confirmatory trials. | Preliminary | ↑ benefit · small | 2 |
Dosing & Compounds
Typical Dose
100–200 mg; often paired 1:2 with caffeine (e.g. 100mg theanine + 50mg caffeine).
Active Compounds
Safety & Cautions
Very safe, no known serious side effects. Non-sedating at typical doses. Educational only — always check with your doctor or pharmacist before combining L-Theanine with any medicine.
Key Studies ★ 16 studies
Meta-analysis
Dasdelen 2025 (meta-analysis)
✓ PubMed
Meta-analysis of 18 RCTs (897 participants) found L-theanine significantly improved subjective sleep quality (SMD 0.43), sleep onset latency (SMD 0.15), and daytime dysfunction (SMD 0.33).
Meta-analysis
Sadowska-Krepa 2025 (meta-analysis)
✓ Full text
Meta-analysis of 5 placebo-controlled RCTs (148 healthy adults) found a dose-dependent improvement in visual processing/reaction time (RVIP) but no consistent benefit across other cognitive tests, calling cognitive effects promising but not conclusive.
Meta-analysis
Nutrition Reviews 2025 (meta-analysis)
✓ Full text
Systematic review/meta-analysis of RCTs found L-theanine plus caffeine produced small-to-moderate improvements in attention-switching and digit-vigilance accuracy and in alertness/mood, with L-theanine alone modestly improving choice reaction time in healthy adults.
Systematic review
Moshfeghinia 2024 (systematic review)
✓ PubMed
Systematic review of 11 RCTs (>800 patients) reported L-theanine supplementation reduced psychiatric symptoms more than controls in schizophrenia, anxiety disorders, and ADHD, while calling for larger confirmatory trials.
systematic review
Walsh 2026 (systematic review)
✓ PubMed
Systematic review of 13 dietary-supplementation trials (n=550; 11 RCTs) concluded that 200-450 mg/day of standalone L-theanine appears safe and effective for supporting healthy sleep in adults, with benefits on objective and self-reported sleep latency, maintenance, efficiency, and feelings of refreshment on waking.
Meta-analysis
Nutrition Reviews 2025
✓ Full text
Meta-analysis of 50 RCTs found small-to-moderate benefits of L-theanine plus caffeine over placebo in the first 2 hours for choice reaction time, attention-switching accuracy, and mood, with L-theanine alone favoring choice reaction time.
Systematic review
BMC Psychiatry 2024
✓ Full text
Systematic review of 11 RCTs (>800 patients) found L-theanine supplementation significantly reduced psychiatric symptoms versus controls in schizophrenia, anxiety disorders, and ADHD, with reductions also seen in depression and Tourette tic severity.
Meta-analysis
Payne et al. 2025 (Nutrition Reviews)
✓ PubMed
Systematic review/meta-analysis of 50 RCTs (15 pooled) in healthy adults: L-theanine alone modestly favored faster choice reaction time vs placebo (SMD -0.35; 95% CI -0.61 to -0.10) at hour 1; L-theanine plus caffeine improved attention-switching accuracy (h2 SMD 0.33; 95% CI 0.13-0.54) and digit-vigilance accuracy (h2 SMD 0.20; 95% CI 0.02-0.38).
Meta-analysis
Matyus et al. 2025 (J Clin Med)
✓ PubMed
Systematic review/meta-analysis of 5 RCTs (148 healthy adults): L-theanine showed a dose-dependent benefit on rapid visual information processing / recognition visual reaction time (MD -15.20 ms; 95% CI -28.99 to -1.41), but no significant effect on simple reaction time or Stroop test; benefits domain-specific and not confirmed across all measures.
Systematic review
Sharma 2021 (systematic review)
✓ Full text
Systematic review of 5 clinical trials concluded the L-theanine plus caffeine combination is likely a safe and effective cognitive enhancer, improving short-term sustained attention and overall cognition.
Systematic review
Williams 2020 (systematic review)
✓ PubMed
Systematic review of 9 RCTs found that 200-400 mg/day of pure L-theanine may help reduce stress and anxiety in people exposed to stressful conditions.
RCT
Moulin 2024 (RCT)
✓ PubMed
Randomized, double-blind, placebo-controlled trial in 30 healthy adults with moderate stress found 28 days of 400 mg/day AlphaWave L-theanine significantly reduced perceived stress, decreased light sleep, improved sleep quality, and enhanced cognitive attention versus placebo, with a good safety profile.
RCT
Hidese et al. 2019 (Nutrients)
✓ PubMed
4-week randomized, placebo-controlled, double-blind crossover trial in 30 healthy adults: L-theanine 200 mg/day reduced depression (SDS), trait anxiety (STAI-T), and sleep problems (PSQI) scores (all p<0.05) and improved verbal fluency and executive function vs placebo.
Study
Hidese 2019
✓ Full text
4 weeks reduced stress-related symptoms and improved cognition.
Study
Owen 2008
✓ PubMed
Theanine + caffeine improved attention-switching and alertness.
Study
Kimura 2007
✓ PubMed
Attenuated physiological stress responses to an acute stressor.