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Evidence-Based Supplement Research

Evidence-Based Supplement Research

L-Theanine and Reduced P3b Latency

Doses used in studies

mg/day: 100–400 (median 225, IQR 125–350) — 2 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

2 of 2 papers

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 P3b Latency
- High evidence
- Adults
the L-theanine-caffeine combination significantly ... reduced the latencies of P3b ERP component
Effect
Beneficial
Effect size
Small
Significant
Yes
Dose
200 mg
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
- Reduced P3b Latency
- High evidence
- Adults
400 mg of theanine showed a significant reduction in the latency of the parietal P3b ERP component (p < 0.05), whereas no significant changes were observed with lower doses. A subsequent exploratory regression showed that each 100-mg increase in dose reduces the P3b latency by 4 ms (p < 0.05).
Effect
Beneficial
Effect size
Small
Significant
Yes
Dose
100, 200 and 400 mg