L-theanine and reaction time: grade B

Moderate evidence. Direction: Benefit.

B ModerateShort-term only

Educational guidance, not medical advice

Why this grade

Rubric condition met: Meta-analyses with a consistent pooled direction but conflicting individual trials (B); A not proposed because individual trials disagree. Context: L-theanine alone, single dose.

A 2026 meta-analysis found a single 200 mg dose improved choice reaction time (SMD 0.51) in healthy adults, and a 2025 industry co-funded meta-analysis found a smaller first-hour effect favoring theanine (SMD -0.35). Individual trials conflict: one small crossover trial found faster recognition reaction time, while a 48-person trial found theanine slowed reaction time on a visual probe task. Single-dose effects only.

How we grade evidence

Studies this grade rests on

each study this grade rests on, by publication year and design. Solid: effect versus the comparator; half-filled: mixed; hollow: no effect; dashed: result not recorded yet. Larger marks had more participants.

Show the numbers

Study	Year	Design	Participants	Result
Rogers 2008	2008	RCT	48	result not recorded
Kahathuduwa 2017	2017	crossover RCT	20	result not recorded
Payne 2025	2025	meta-analysis	not recorded	result not recorded
Gerolymos 2026	2026	meta-analysis	1168	result not recorded

Acute effects of theanine, caffeine and theanine-caffeine combination on attention.

Kahathuduwa CN, Dassanayake TL, Amarakoon AMT. Acute effects of theanine, caffeine and theanine-caffeine combination on attention Nutr Neurosci, 2017. PMID 26869148

Result not recorded

Design: Placebo-controlled five-way crossover trial (acute)
Sample: n = 20
Population: Healthy male volunteers
Funding: National Research Council Grant, Sri Lanka

Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together.

Rogers PJ, Smith JE, Heatherley SV. Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together Psychopharmacology (Berl), 2008. PMID 17891480

Result not recorded

Design: Randomized, double-blind, placebo-controlled trial (acute)
Sample: n = 48
Population: Healthy adults
Funding: not stated in PubMed record

Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.

Payne ER, Aceves-Martins M, Dubost J. Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of Randomized Controlled Trials Nutr Rev, 2025. PMID 40314930

Result not recorded

Design: Systematic review (50 RCTs) and meta-analysis (15 eligible)
Population: Healthy participants
Funding: Analytical Services Division RI-B5-06, Lipton Teas and Infusions, Scottish Government Rural and Environment Science, Scottish Government Rural and Environment Science and Analytical Services Division, Scottish Government Rural and Environment Science and Analytical Services Division RI-B5-06

Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials.

Gerolymos C, Saddier E, Boyer L. Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials Mol Psychiatry, 2026. PMID 42410082

Result not recorded

Design: Systematic review and meta-analysis of 31 randomized placebo-controlled trials
Sample: n = 1,168
Population: Healthy and clinical populations (primary outcome: healthy adults, single dose)
Funding: not stated in PubMed record

Search and history

Search (November 11, 2026): theanine[ti] AND (meta-analysis[pt] OR systematic review[pt])

November 11, 2026 Graded B (proposed): Proposed in the monograph draft
November 13, 2026 B to B (approved): Editor sign-off November 13, 2026: grade matches the editor-approved final page