New evidence
A meta-analysis of 9 studies linked L-theanine to a moderate reduction in daytime dysfunction (SMD 0.33) — but the evidence is still early and the dose wasn't specified.
This is one of the first meta-analyses to suggest L-theanine may help with daytime sleepiness, but because the underlying studies were not blinded and the dose varied, the result should be considered preliminary.
Researchers pooled 9 studies and found that people taking L-theanine reported less trouble staying awake and functioning during the day, with a moderate effect size. However, the studies lacked blinding, the exact dose used wasn't reported, and this is among the first analyses on this topic — so the finding needs confirmation in more rigorous trials.
Where this fits in the evidence
This is among the first studies we've indexed on L-Theanine for Improved Daytime Dysfunction — treat it as an early signal until more research accumulates.
The study
The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis.
- Meta-Analysis
- n = 897
- 2025-06
- Sleep medicine reviews
This is a plain-language summary of a research finding, not medical advice. Pillser surfaces research signals to help you decide what's worth investigating — always consult a qualified professional before changing what you take.