L-theanine and sleep quality: grade C

Limited evidence. Direction: Benefit.

C LimitedSubjective outcome onlyIndustry-funded

Educational guidance, not medical advice

Why this grade

Rubric condition met: Meta-analysis significant only for subjective outcomes, pooling people of all ages and health status and non-pure products; healthy-adult trials are small and supplier-funded (C, conservative). Grader to confirm against B (meta-analysis with high heterogeneity; heterogeneity not reported in the abstract).

A 2025 meta-analysis of 18 trials in people of all ages and health status found small improvements in self-rated sleep quality, time to fall asleep and daytime dysfunction, but noted a lack of studies on pure L-theanine. A 2026 systematic review by tobacco-industry researchers reported benefits across 13 trials. In healthy adults the trials are small and supplier-funded, and one 28-day trial recorded less time asleep with L-theanine.

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
Hidese 2019	2019	crossover RCT	30	result not recorded
Moulin 2024	2024	RCT	30	result not recorded
Bulman 2025	2025	meta-analysis	897	result not recorded
Cotter 2026	2026	systematic review	550	result not recorded

Examining the effect of L-theanine on sleep: a systematic review of dietary supplementation trials.

Cotter J, Caddick CE, Harper JL. Examining the effect of L-theanine on sleep: a systematic review of dietary supplementation trials Nutr Neurosci, 2026. PMID 41176609

Result not recorded

Design: Systematic review of 13 trials (11 RCTs, 2 single-arm open-label)
Sample: n = 550
Population: Adults
Funding: not stated in PubMed record

Safety and Efficacy of AlphaWave(®) L-Theanine Supplementation for 28 Days in Healthy Adults with Moderate Stress: A Randomized, Double-Blind, Placebo-Controlled Trial.

Moulin M, Crowley DC, Xiong L. Safety and Efficacy of AlphaWave(®) L-Theanine Supplementation for 28 Days in Healthy Adults with Moderate Stress: A Randomized, Double-Blind, Placebo-Controlled Trial Neurol Ther, 2024. PMID 38758503

Result not recorded

Design: Randomized, double-blind, placebo-controlled trial (28 days)
Sample: n = 30
Population: Healthy adults 18-65 with moderate stress
Funding: Ethical Naturals, Inc. (Crossref funder)

Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial.

Hidese S, Ogawa S, Ota M. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial Nutrients, 2019. PMID 31623400

Result not recorded

Design: Randomized, placebo-controlled, crossover, double-blind trial (4 weeks)
Sample: n = 30
Population: Adults without major psychiatric illness, mean age 48.3
Funding: Funding received from Taiyo Kagaku Co., Ltd., Mie, Japan., Funding received from Taiyo Kagaku Co., Ltd., Mie, Japan. None

The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis.

Bulman A, D'Cunha NM, Marx W. The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis Sleep Med Rev, 2025. PMID 40056718

Result not recorded

Design: Systematic review and meta-analysis (19 articles, 18 meta-analysed)
Sample: n = 897
Population: All ages and health status (healthy and clinical)
Funding: University of Canberra

Search and history

Search (November 11, 2026): theanine[ti] AND sleep[tiab] AND (randomized controlled trial[pt] OR clinical trial[pt] OR meta-analysis[pt] OR systematic review[pt])

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