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L-theanine alone shaved choice reaction time by a moderate amount in a meta-analysis — but the confidence interval suggests the true effect could be small.
This is one of the first pooled analyses on theanine for cognition, so the finding is promising but far from settled; the moderate effect size comes with enough uncertainty that a person might notice little to no difference in real life.
A meta-analysis of randomized trials found that L-theanine, taken alone or with caffeine, improved choice reaction time — a measure of how quickly someone can respond correctly to a changing signal — compared to placebo. The effect was moderate (standardized mean difference -0.35), but the confidence interval (-0.61 to -0.10) means the real benefit could be anywhere from modest to barely noticeable. Because this is among the first meta-analyses on theanine specifically, the finding needs replication before it can be considered solid.
Where this fits in the evidence
This is among the first studies we've indexed on L-Theanine for Improved Choice Reaction Time — treat it as an early signal until more research accumulates.
The study
- Meta-Analysis
- 2025-05-02
- Nutrition reviews
- PubMed: 40314930
- DOI: 10.1093/nutrit/nuaf054
- Full study breakdown →
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