L-Theanine and Improved Attention Span

Research synthesisLow evidenceMixed effect size3 studies · 2 beneficial · 1 neutral · 0 harmful

Across 3 studies, 2 reported beneficial effects and 1 found neutral results, with the beneficial effects being small to large in magnitude. The most-studied dose range was approximately 100–400 mg, often as a single dose, in adult populations including athletes and middle-aged/older adults. The median study duration was 84 days, but only 1 of 3 studies reported duration, limiting the strength of this finding.

Effective dose range: 100–400 mg single dose
Studied populations: adults, athletes, middle-aged and older adults (50–69 years)

Caveats: Evidence base is small (only 3 studies) — conclusions should be considered preliminary. The single neutral study (2022) found no effect on neurophysiological measures, suggesting inconsistency in outcomes. One beneficial study (2023) used a very low dose (6 mg/kg) combined with caffeine, which may confound the specific L-theanine effect. No data on supplement form (e.g., free-form vs. other) were reported in any study.

Generated Jun 12, 2026

Doses used in studies

mg/day: 100–400 (median 250, IQR 100–400) — 1 study
mg/kg single-dose: 6 (median 6, IQR 6–6) — 1 study

Time to effect

Median: 2.8 months · IQR 2.8 months–2.8 months · Range 2.8 months–2.8 months — Reported in 1 of 3 studies

Safety in these studies

Overall tolerabilityReported
L-theanine, a non-proteinic amino acid found in tea, is known to enhance attention particularly in high doses, with no reported adverse effects.
from: L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a

3 of 3 papersPopulation:

Effect of single or combined caffeine and L-Theanine supplementation on shooting and cognitive performance in elite curling athletes: a double-blind, placebo-controlled study.
- 2023-10-10
- RCT
- Journal of the International Society of Sports Nutrition 20(1)
- - Umut Yilmaz
  - Yusuf Buzdagli
  - Muhammed Lütfü Polat
  - Yusuf Bakir
  - Burak Ozhanci
  - Sena Alkazan
  - Halil Ucar
- PubMed: 37815006
- DOI: 10.1080/15502783.2023.2267536
11 Insights on
- Improved Attention Span
- High evidence
- Athletes
The best reaction times during ... ICR ... tasks were achieved with the combined CAF and THE intake, showing a significant improvement compared to PLA
Effect
Beneficial
Effect size
Large
Significant
Yes
Dose
6 mg/kg single dose
L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover study.
- 2020-08-11
- RCT
- Nutritional neuroscience 25(4)
- - Tharaka L Dassanayake
  - Chanaka N Kahathuduwa
  - Vajira S Weerasinghe
- PubMed: 32777998
- DOI: 10.1080/1028415x.2020.1804098
4 Insights on
- Improved Attention Span
- High evidence
- Adults
No dose-response effect was observed in P3b amplitude, pre-attentive ERP components or reaction time.
Effect
Neutral
Effect size
Small
Significant
No
Dose
100, 200 and 400 mg
Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study.
- 2021-04
- RCT
- Journal of medicinal food 24(4)
- - Yoshitake Baba
  - Shun Inagaki
  - Sae Nakagawa
  - Toshiyuki Kaneko
  - Makoto Kobayashi
  - Takanobu Takihara
- PubMed: 33751906
- DOI: 10.1089/jmf.2020.4803
5 Insights on
- Improved Attention Span
- High evidence
- Adults
The single dose of l-theanine reduced the reaction time to attention tasks (Stroop test, Part 1)
Effect
Beneficial
Effect size
Small
Significant
Yes
Dose
single dose

L-Theanine and Improved Attention Span

Effect of single or combined caffeine and L-Theanine supplementation on shooting and cognitive performance in elite curling athletes: a double-blind, placebo-controlled study.

L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover study.

Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study.