L-Theanine

Theanine

Snapshot

Indications	Contraindications
Stress and anxiety¹ Sleep quality² Attention with caffeine³ Insomnia in cancer patients⁴ Adjunct in schizophrenia⁵ Major depressive disorder (add-on)⁶	Pregnancy and lactation⁷ Green tea hypersensitivity⁷

L-theanine is a water-soluble amino acid found in green tea and some mushrooms⁷. It crosses into the brain and promotes calm through inhibitory neurotransmission and alpha-wave activity⁷. People take it for stress and anxiety¹, sleep quality, and attention when paired with caffeine³. Clinicians also study it as an adjunct in psychiatric disorders⁸.

Randomized trials pooled in a meta-analysis found better subjective sleep quality, though studies of pure L-theanine are few². In treatment-resistant obsessive-compulsive disorder, a 2022 open-label pilot of a combination including L-theanine reported symptom reductions without a placebo control⁹. More than 3,000 products listing L-theanine are on the US market, mostly capsules; see Form comparison.

Per the Memorial Sloan Kettering monograph, L-theanine with sleep medications such as lorazepam, diazepam, or zolpidem may increase drowsiness, and it advises talking with a healthcare provider before combining them⁷.

Last updated October 15, 2026. Read how we make monographs.

In the full monograph

72 sources, 52 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources