Examining the effect of L-theanine on sleep: a systematic review of dietary supplementation trials.
Level 1 - systematic review of randomized trials
Systematic review of predominantly randomized controlled trials
PubMed 41176609 · doi:10.1080/1028415X.2025.2556925
What was done
A systematic review searching Ovid MEDLINE, PsycINFO, Embase, CENTRAL, and Google Scholar through February 3, 2025, evaluated human trials assessing standalone L-theanine supplementation (50-900 mg/day) on sleep-related outcomes. Articles were independently screened by three authors.
What was found
Thirteen trials with a combined total of 550 participants met inclusion criteria (11 randomized controlled trials and 2 single-arm, open-label trials). The authors reported beneficial effects on objective and subjective metrics, including sleep latency, sleep maintenance, sleep efficiency, perceived sleep satisfaction, and feelings of refreshment and recovery on waking, primarily at dosages of 200-450 mg/day. Numerical effect sizes, confidence intervals, and statistical significance values were not reported in the abstract.
Why it matters
This review synthesizes human clinical evidence regarding L-theanine as a non-prescription dietary supplement for improving sleep quality and daytime recovery.
Limits
The total sample size across 13 trials is small (550 participants total, averaging ~42 participants per trial). Two included studies were open-label without control arms, and data in clinical insomnia populations were noted as an ongoing research gap.
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