theanine

Theanine, commonly referred to as L-theanine, is an amino acid analogue (N-ethyl-L-glutamine) found naturally in the leaves of Camellia sinensis, the tea plant, and in smaller amounts in some mushrooms. It is a non-proteinogenic amino acid and is not incorporated into proteins.

In humans, theanine crosses the blood-brain barrier and is thought to influence brain chemistry by modulating several neurotransmitters, including GABA, dopamine, and serotonin, as well as glutamate activity. It is also associated with increased alpha-band activity on EEG, a brain pattern linked to relaxed alertness.

Uses and effects: Theanine is marketed as a dietary supplement for relaxation, stress relief, and cognitive performance. Some randomized trials suggest modest improvements in attention and reaction time when theanine is combined with caffeine, but evidence is inconsistent. Some studies report better sleep quality in people with anxiety, but findings are not conclusive.

Safety and regulation: Theanine is generally well tolerated at common supplement doses (roughly 100-400 mg per day). Side effects are rare. Data on pregnancy and lactation are insufficient; consult a clinician. Potential interactions include sedatives and medications that affect blood pressure or alertness.

Chemistry and sources: Theanine can be isolated from tea leaves or produced synthetically. Tea intake provides varying amounts depending on variety and preparation. It appears widely in dietary supplement products and is not marketed as a medicine, though it is used for purported relaxation and cognitive benefits.