← All sources
Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial
Japanese double-blind, placebo-controlled crossover trial (n=30 healthy adults without major psychiatric illness): 200 mg/day L-theanine for four weeks vs placebo improved self-rated depression, trait anxiety, and global PSQI sleep quality versus placebo, with several PSQI subscales (sleep latency, sleep disturbance, sleep medication use) favoring theanine; verbal fluency and executive-function scores also improved, with stronger letter-fluency gains in the lower-baseline subgroup.
Design
- Population: 30 adults (9 M / 21 F), mean age 48.3 ± 11.9 y, no major psychiatric illness
- Intervention: 200 mg/day L-theanine tablets vs matched placebo
- Schedule: 4-week blinded arms in a crossover layout (each participant serves as own control)
- Primary stress readouts: Self-rating Depression Scale (SDS), STAI trait, PSQI
- Cognitive battery: verbal fluency (letter/category) and executive-function tasks
Key outcomes (trial-reported significance)
- SDS, STAI-trait, PSQI total: each lower after L-theanine vs placebo (p = 0.019, 0.006, 0.013)
- PSQI subscales for sleep latency, sleep disturbance, and sleep medication use: improved vs placebo (all p < 0.05)
- Verbal fluency & executive function: higher after L-theanine (p = 0.001 and 0.031); letter fluency showed the clearest subgroup signal when stratified by median baseline performance (p = 0.002)
Interpretation for this wiki
- Anchors oral 200 mg/day dosing used elsewhere on
l-theanine-supplementation(forum N=1) with a crossover RCT rather than a large parallel-group outcomes trial. - Sleep metrics here are questionnaire-tier (PSQI), not polysomnography—pair with
sleep-optimizationPubMed rows when readers need PSG/CBT-i evidence.
Conflicts / funding
Abstract lists Taiyo Kagaku Co., Ltd. employees among authors (tablets supplied by industry); treat as efficacy signal under sponsorship, not neutral public-health proof alone.
Outcomes
- Depression & Anxiety Composite ScoreAfter 200 mg/day L-theanine vs placebo: lower Self-rating Depression Scale (p = 0.019) and STAI trait anxiety (p = 0.006) in the crossover analysis.
- Pittsburgh Sleep Quality Index Scorepoints (Points)
- Cognitive battery: verbal fluency and executive-function scores improved vs placebo (p = 0.001 and p = 0.031); letter-fluency gain strongest among lower-baseline performers (p = 0.002 vs placebo in median split).