What is L-theanine?

L-theanine is a non-protein amino acid found mainly in tea leaves. It is commonly used for relaxation, attention and sleep support rather than muscle-protein synthesis.

It may produce a calming effect without strong sedation, although individual responses vary.

Stress and attention

A 2026 meta-analysis of 31 randomized trials found that a single 200 mg dose taken 30–60 minutes before testing improved choice reaction time. Effects on acute stress were modest, while anxiety outcomes remained inconsistent.

L-theanine may therefore support attention or mild relaxation, but it is not an established treatment for anxiety or depression.

L-theanine with caffeine

The combination has stronger evidence for acute focus than L-theanine alone.

A trial using 97 mg of L-theanine with 40 mg of caffeine reported improved attention during a demanding cognitive task. A 2025 meta-analysis also found small-to-moderate benefits in selected attention, accuracy and mood outcomes during the first two hours after intake.

The combination may be found in pre-workout supplements, but L-theanine does not eliminate caffeine-related insomnia, nervousness or rapid heartbeat.

Sleep

A systematic review of 13 trials reported possible improvements in sleep latency, maintenance, efficiency and morning refreshment. The most practical evidence involved approximately 200–450 mg per day, although additional independent trials are required.

L-theanine may be included in sleep-support products, but it is not a treatment for chronic insomnia or sleep apnoea.

Dosage and safety

Common research amounts include:

• 100–200 mg for relaxation or attention,
• 200 mg approximately 30–60 minutes before cognitive work,
• 200–450 mg per day in sleep studies,
• up to 400 mg per day in short-term stress studies.

Short-term studies suggest good tolerability, but no official upper intake level has been established for long-term supplementation.

EFSA considers up to 400 mg of caffeine per day to be of no concern for most healthy adults. However, even 100 mg close to bedtime may disturb sleep.

Professional guidance is appropriate during pregnancy, breastfeeding, with low blood pressure or when using sedatives or blood-pressure medication.

Conclusion

L-theanine may support calm attention without strong sedation. Its most consistent cognitive effects appear when it is combined with caffeine.

Evidence for sleep is promising, but L-theanine should not replace medical assessment for persistent anxiety or sleep disorders.

References

1. Gerolymos C et al. Cognitive and Affective Effects of L-Theanine: A Systematic Review and Meta-Analysis of 31 Randomized Trials. Published July 6, 2026.
2. Payne ER et al. Effects of Tea, L-Theanine or L-Theanine Plus Caffeine on Cognition, Sleep and Mood. Published in the October 1, 2025 issue.
3. Cotter J et al. Examining the Effect of L-Theanine on Sleep. Published online November 1, 2025; issue date February 2026.
4. Moulin M et al. Safety and Efficacy of L-Theanine Supplementation for 28 Days. Published May 17, 2024.
5. Giesbrecht T et al. L-Theanine and Caffeine Improve Cognitive Performance and Alertness. Published 2010.
6. EFSA NDA Panel. Scientific Opinion on the Safety of Caffeine. Published May 27, 2015.