Story perspectives

200 mg L-theanine Improves Reaction Time, Reduces Stress

7/6/2026

Summary

Story summary

A review of 31 trials (1,168 participants) found a single 200 mg L-theanine dose improved choice reaction time (SMD = 0.51; 95 % CI 0.25–0.77).
The same dose yielded a modest acute stress reduction (SMD = 0.31), an effect driven by high-bias studies.
No significant impact on fatigue was observed, with dropout rates matching placebo and no serious adverse events.
Excluding one outlier, the dose reduced depressive symptoms in healthy adults (SMD = 0.69; 95 % CI 0.13–1.25).

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Story summary

A review of 31 trials (1,168 participants) found a single 200 mg L-theanine dose improved choice reaction time (SMD = 0.51; 95 % CI 0.25–0.77).
The same dose yielded a modest acute stress reduction (SMD = 0.31), an effect driven by high-bias studies.
No significant impact on fatigue was observed, with dropout rates matching placebo and no serious adverse events.
Excluding one outlier, the dose reduced depressive symptoms in healthy adults (SMD = 0.69; 95 % CI 0.13–1.25).