L-theanine is a unique amino acid found almost exclusively in the tea plant (Camellia sinensis) and contributes to the unusual taste of green tea.

Human studies have shown that taking L-theanine affects the emission of alpha waves in the brain, associated with states of relaxation and focused attention.

Preliminary research has shown that L-theanine crosses the blood-brain barrier and suggests that it may promote healthy levels of neurotransmitters in the brain and inhibit the stimulating properties of caffeine.