Amino AcidsL-Theanine

L-theanine supplementation improves subjective sleep quality, reduces sleep onset latency, and decreases daytime dysfunction.

A systematic review and meta-analysis of 19 RCTs (N=897 participants) found that L-theanine significantly improved subjective sleep onset latency (SMD=0.15, 95% CI [0.01, 0.29], p=0.04), subjective daytime dysfunction (SMD=0.33, 95% CI [0.16, 0.49], p<0.001), and overall subjective sleep quality score (SMD=0.43, 95% CI [0.04, 0.83], p=0.03). The findings suggest potential use for managing sleep disturbances, but further research is needed on pure L-theanine and optimal dosing.

Last updated: Jul 7, 2026•0 RCTs•1 Meta-analyses•📖 Read as article →

Evidence Score

Evidence Score53/100
Human RCT☆☆☆☆☆
Meta-analysis★★★☆☆
Mechanism★★★★★
Safety★★★★☆
Confidencelow

Study Evidence

Study 1. The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis.

observational

Bulman A, D'Cunha NM, Marx W, Turner M, McKune A, Naumovski N · Sleep medicine reviews (2025)

Participants: N/A
Duration: N/A (varies across included studies)
Intervention: L-theanine supplementation (various doses and durations across included studies)
Outcome: Subjective sleep onset latency, subjective daytime dysfunction, overall subjective sleep quality score (measured via validated questionnaires)
Effect Size: SMD=0.43 for overall sleep quality; SMD=0.15 for sleep onset latency; SMD=0.33 for daytime dysfunction
Population: Humans of all ages and health status (N=897 participants across 19 studies)

Result:

PubMed: 40056718DOI: 10.1016/j.smrv.2025.102076

Mechanism Graph

L-theanine is a non-proteinogenic amino acid found in tea
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It may promote relaxation by increasing GABA, serotonin, and dopamine levels
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It reduces stress and anxiety, which can interfere with sleep
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Result: Improved subjective sleep quality and reduced sleep onset latency

Limitations

  • ⚠Lack of studies on 'pure' L-theanine (many studies may have used combination products)
  • ⚠Insufficient data to determine adequate dose and duration for improving sleep quality

Frequently Asked Questions

What is L-theanine and where is it found?▼

L-theanine is a non-proteinogenic amino acid primarily found in tea leaves, especially green tea. It is known for its calming effects.

How does L-theanine improve sleep?▼

L-theanine may improve sleep by promoting relaxation through modulation of neurotransmitters like GABA, serotonin, and dopamine, and by reducing stress and anxiety.

What sleep outcomes did L-theanine improve in this meta-analysis?▼

The meta-analysis showed significant improvements in subjective sleep onset latency, daytime dysfunction, and overall subjective sleep quality score.

Is L-theanine safe for all populations?▼

The abstract included participants of all ages and health status, but specific safety data and optimal dosing were not provided, so caution is warranted, especially for clinical populations.

Products

Affiliate links coming soon. We only recommend products that match the doses and forms used in the cited research.

References

  1. 1.Bulman A, D'Cunha NM, Marx W, Turner M, McKune A, Naumovski N. "The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis.." Sleep medicine reviews, 2025. PMID: 40056718 DOI: 10.1016/j.smrv.2025.102076
Disclaimer: This content is for educational purposes only and is not medical advice. Evidence scores reflect the quality and quantity of available research, not clinical recommendations. Always consult a healthcare professional before starting any supplement or intervention.