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

source extracted confidence: high 2026-04-09
#humans #glutamates #dietary-supplements #sleep #randomized-controlled-trials-as-topic

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

Cotter et al., 2026 | Nutr Neurosci | Systematic Review

Citation

Cotter Jack, Caddick Charlotte E, ... Ebajemito James K. Examining the effect of L-theanine on sleep: a systematic review of dietary supplementation trials. Nutr Neurosci. 2026-Feb;29(2):224-238. doi:10.1080/1028415X.2025.2556925

Abstract

Objective: Sleep problems are a common complaint among adults worldwide, however, the use of prescription and over-the-counter products may not always be an appropriate or desirable solution. L-theanine is a naturally occurring, non-protein amino acid that can be found in the leaves of the tea plant Camellia sinensis. Previous studies have reported that consumption of L-theanine can help to aid relaxation, without causing sedation or adversely impacting cognitive function. Building on these calming effects and results from recent pre-clinical studies, the aim of this review was to systematically appraise the scientific literature to establish whether dietary supplementation with L-theanine can also help to support sleep in humans.Methods: Electronic database searches of Ovid MEDLINE, PsycINFO, Embase, CENTRAL and Google Scholar were conducted from inception to 3rd February 2025. Retrieved articles were independently reviewed by three authors.Results: Thirteen eligible trials (n = 550) that examined the effect of L-theanine (50-900 mg/day) as a standalone intervention on sleep-related outcome measures were identified. This included two single-arm, open-label trials and eleven randomised controlled trials.Discussion: Based on the current evidence, supplementation with 200-450 mg/day of L-theanine appears to be a safe and effective way to support healthy sleep in adults. Among the included trials, beneficial effects were reported on both objective and participant-reported outcomes, including measures linked to sleep latency, maintenance and efficiency, perceived sleep satisfaction and feelings of refreshment and recovery on waking. Further high-quality trials using objective measures, into the mechanisms underlying these effects, and among those with clinical insomnia would provide further useful insights.

Key Findings

Thirteen eligible trials (n = 550) that examined the effect of L-theanine (50-900 mg/day) as a standalone intervention on sleep-related outcome measures were identified. This included two single-arm, open-label trials and eleven randomised controlled trials.Discussion: Based on the current evidence, supplementation with 200-450 mg/day of L-theanine appears to be a safe and effective way to support healthy sleep in adults. Among the included trials, beneficial effects were reported on both object

Outcomes Measured

  • Requires manual extraction

Population

Field Value
Population See abstract
Sample Size 550
Age Range See abstract
Condition insomnia

MeSH Terms

  • Humans
  • Glutamates
  • Dietary Supplements
  • Sleep
  • Randomized Controlled Trials as Topic
  • Sleep Wake Disorders
  • Adult

Evidence Classification

  • Level: Systematic Review
  • Publication Types: Journal Article, Systematic Review, Review
  • Vertical: l-theanine-sleep

Provenance

Source extracted via PubMed E-utilities API on 2026-04-09