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 of L-theanine on attention span, with effect sizes ranging from small to large. The predominant effect direction is beneficial, but effect sizes are mixed (small to large). The most studied population is healthy adults, including athletes and middle-aged/older individuals, with single doses commonly tested. Evidence is too limited to establish a typical dose range or duration.

Studied populations: elite athletes, healthy young adults, middle-aged and older adults (50-69 years)

Caveats: Evidence base is small (only 3 studies) — conclusions should be considered preliminary. One study found no significant effect on attention-related neurophysiological measures despite using multiple doses, contradicting the beneficial results from the other two trials. The beneficial study in athletes combined L-theanine with caffeine, which may confound the independent effect of L-theanine.

Generated Jul 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.