L-Theanine and Reduced Reaction Time

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

Across 3 studies, 2 reported beneficial effects of L-theanine on reducing reaction time, with effect sizes ranging from small to large; 1 study found no significant difference versus placebo. The most-studied dose was 200 mg, often in sleep-deprived young adults. Effects were observed both acutely and over 84 days, though the evidence base is small.

Effective dose range: 200 mg (single dose)
Studied populations: sleep-deprived young adults (aged 20–30 years), middle-aged and older adults (aged 50–69 years)

Caveats: Evidence base is small (only 3 studies) — conclusions should be considered preliminary. One study used a caffeine combination rather than L-theanine alone, which may confound the effect. Another study reported no significant between-group difference in reaction time despite within-group improvements. Most studies focused on sleep-deprived populations, so generalizability to rested individuals is unclear.

Generated Jul 12, 2026

Doses used in studies

mg/day: 200 (median 200, IQR 200–200) — 2 studies

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

3 of 3 papers

Effect of L-theanine on selective attention in a traffic-related reaction task in sleep-deprived young adults: a double-blind placebo-controlled, crossover study.
- 2024-07-25
- RCT
- Nutritional neuroscience 28(4)
- - Umangi W Karunaratne
  - Tharaka L Dassanayake
- PubMed: 39052627
- DOI: 10.1080/1028415x.2024.2383080
4 Insights on
- Reduced Reaction Time
- High evidence
- Adults
L-theanine reduced hit reaction time by 38.65 ms (p = 0.007), and placebo by 19.08 ms (p = 0.016), however reaction time changes from baseline were not significantly different between treatments (p > 0.05)
Effect
Neutral
Effect size
Small
Significant
No
Dose
200 mg
High-dose L-theanine-caffeine combination improves neurobehavioural and neurophysiological measures of selective attention in acutely sleep-deprived young adults: a double-blind, placebo-controlled crossover study.
- 2025-08-12
- RCT
- The British journal of nutrition 134(3)
- - Gayani S Nawarathna
  - Dewasmika I Ariyasinghe
  - Tharaka L Dassanayake
- PubMed: 40789769
- DOI: 10.1017/s0007114525104169
5 Insights on
- Reduced Reaction Time
- High evidence
- Adults
the pre-post-dose reaction time improvement of the L-theanine-caffeine combination was significantly greater than that of placebo (△ = 38·1 ms, P = 0·003)
Effect
Beneficial
Effect size
Large
Significant
Yes
Dose
200 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
- Reduced Reaction Time
- 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 (exact dose not specified)

L-Theanine and Reduced Reaction Time

Effect of L-theanine on selective attention in a traffic-related reaction task in sleep-deprived young adults: a double-blind placebo-controlled, crossover study.

High-dose L-theanine-caffeine combination improves neurobehavioural and neurophysiological measures of selective attention in acutely sleep-deprived young adults: 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.