L-theanine

Also known as theanine, l theanine, suntheanine.

Last reviewed October 9, 2026 · Jump to references

What is L-theanine?

In plain words

L-theanine is an amino acid found in tea that the body does not use to build proteins. The body absorbs it, and some reaches the brain before being broken down. Researchers study it for relaxation, stress, sleep, and attention, sometimes together with caffeine. Human studies suggest possible benefits, but many are small and short, so lasting effects and long-term safety are less clear.

Technical definition

L-theanine (γ-glutamylethylamide) is a non-proteinogenic amino acid found naturally in tea leaves and structurally related to glutamate. It crosses the blood–brain barrier and may modulate glutamatergic neurotransmission through interactions with glutamate receptors, although its mechanisms in humans remain incompletely established. In the United States, it is marketed as a dietary supplement, not an FDA-approved drug.

Educational information only. This page does not provide medical advice or determine whether a supplement is appropriate for you. Review supplements with a qualified healthcare professional, especially if you take medication, are pregnant, have surgery scheduled, or have a chronic medical condition.

Evidence by use

Each use is rated on its own. There is no single overall effectiveness score.