11/04/2026
Angela Blackley
Pay Attention! L-Theanine Can Help.
New research suggests that L-theanine can benefit cognition by helping attention and that it can help depression.
L-theanine is an amino acid found almost exclusively in green tea. It improves calm by increasing alpha brain waves, which leads to relaxation and better focus.
That ability of L-theanine has been shown to help improve sleep. New research shows that it can also help improve concentration.
The meta-analysis of 31 controlled studies, which included 1168 people, compared L-theanine to placebo. It found that a single 200mg dose improves choice reaction time, suggesting that it enhances attention.
A single dose also appeared to significantly reduce depression.
L-theanine was safe.
This study suggests that taking a single dose of L-theanine offers short term benefit for attention and depression.
Study below,
Epub 2026 Jul 6.
Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials
Cyril Gerolymos 1, Elisa Saddier 2, Laurent Boyer 2 3, Guillaume Fond 2 3
Affiliations Expand
PMID: 42410082 DOI: 10.1038/s41380-026-03727-9
Abstract
Background: L-theanine, an amino acid derived from green tea, has been suggested to alleviate affective symptoms and enhance cognitive performance, but its clinical relevance remains uncertain.
Methods: We conducted a systematic review and meta-analysis of 31 randomised controlled trials (n = 1168) comparing oral L-theanine with placebo in healthy and clinical populations. The primary outcome was the acute effect of a single dose on stress in healthy adults. Secondary outcomes included clinical measures (stress after repeated dosing, anxiety, depressive symptoms, and fatigue) and cognitive measures (reaction times and attention tasks with single and repeated doses). Safety was assessed by comparing dropout rates and reasons between L-theanine and placebo groups.
Results: A single 200 mg dose taken 30-60 min before cognitive testing significantly improved choice reaction time (Standardised Mean Difference [SMD] = 0.51; 95% CI, 0.25-0.77), indicating enhanced attention. The reduction in acute stress was modest (SMD = 0.31) and largely influenced by studies with a high risk of bias. No significant effect on fatigue was observed. Excluding one outlier, a significant reduction in depressive symptoms following a single dose in healthy individuals was found (SMD = 0.69; 95% CI, 0.13-1.25) with low heterogeneity. Anxiety effects were inconsistent and non-significant except for one study on psychotic anxiety (SMD = 0.54; 400 mg/day for 8 weeks). No serious adverse events were reported.
Conclusions: L-theanine is safe and shows a robust short-term benefit on attention in healthy adults, with a potential antidepressant effect warranting confirmation in high-quality trials, especially in clinical populations.
Ā© 2026. The Author(s), under exclusive licence to Springer Nature Limited.
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Conflict of interest statement
Competing interest: Dr Guillaume Fond founded a company selling dietary supplements. The other authors report no conflicts of interest. Ethics approval and consent to participate: All included randomized controlled trials reported approval by an appropriate ethics committee and obtained informed consent from participants, as required by local regulations.