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Evidence-Based Supplement Research
Evidence-Based Supplement Research
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L-Theanine and Reduced Reaction Time

Research synthesisLow evidenceMixed effect size3 studies · 2 beneficial · 1 neutral · 0 harmful

Across 3 studies, 2 reported beneficial effects of L-theanine on reduced reaction time, with effect sizes ranging from small to large. The evidence is preliminary and primarily limited to sleep-deprived young adults, with doses of 200 mg showing potential acute benefits. One study reported a neutral finding, noting that L-theanine did not significantly differ from placebo despite within-group improvements.

  • Effective dose range: 200 mg single dose
  • Studied populations: sleep-deprived young adults (20–30 years), middle-aged and older Japanese adults (50–69 years)

Caveats: Evidence base is small (only 3 studies) — conclusions should be considered preliminary. Two studies involved overnight sleep-deprived populations, which may limit generalizability to rested individuals. One study used a combination with caffeine, making it difficult to isolate the effect of L-theanine alone. All studies were RCTs but had small sample sizes.

Generated Jun 12, 2026
Doses used in studies
  • mg/day: 200 (median 200, IQR 200–200) — 2 studies
Time to effect
Median: 2.8 months · IQR 2.8 months–2.8 months · Range 2.8 months–2.8 months — Reported in 1 of 3 studies
3 of 3 papers
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