Helps Reduce Anxiety Dietary Supplement L-Theanine is a unique amino acid found almost exclusively in the tea plant (Camellia sinensis) and is the primary ingredient contributing to the unusual taste of green tea. Animal studies have shown that L-theanine crosses the blood brain barrier, increases dopamine and GABA levels in the brain and inhibits the stimulatory properties of caffeine. Human studies have shown that taking L-theanine results in the emission of brain waves associated with a state of relaxation.