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L-Theanine

Also known as Theanine

What it is: Amino acid found in tea
What it does: Promotes alpha-wave activity and modulates excitatory neurotransmission
Status: Widely used supplement
Evidence: Moderate. Moderate human data.
Uses: Calm focus; stress support; sleep support

Caution. Generally well tolerated; may enhance caffeine effects when combined.

Summary

L-theanine is an amino acid found in tea that crosses the blood-brain barrier and influences alpha-wave activity and excitatory neurotransmission. It is often used to promote calm focus, reduce perceived stress, and support sleep quality, and is frequently combined with caffeine for a balanced alert-but-calm state. It is generally well tolerated with a good safety profile.

Checked Jul 19, 2026.

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This entry summarises published information in plain language. It is not medical advice, a dosing recommendation or a substitute for a qualified healthcare professional. Many peptides are not approved for human use, and legal status varies by country. Check anything you rely on against primary sources.