L-theanine is a nonessential amino acid that comes from tea leaves (Camellia sinensis). As it is digested in your small intestine, L-theanine stimulates your brain's production of alpha waves, which make you feel relaxed but alert and not drowsy. L-theanine also helps you stay relaxed by stimulating your body to produce other calming amino acids, such as dopamine, GABA, and tryptophan.
In a study published in a Japanese journal in 1998, researchers measured alpha brain waves in eight students with either high or low anxiety. Students were given plain water for the first and fourth weeks, 50 mg of L-theanine mixed in water the second and fifth weeks, and 200 mg of L-theanine mixed in water the third and sixth weeks. All subjects released larger alpha waves and felt less stressed when they took the 200 mg of L-theanine. Alpha waves increased slightly when subjects took 50 mg. No change took place with only plain water.
A review study on L-theanine in Trends in Food Science and Technology in 1999 confirmed how L-theanine works. The study reported that the brain absorbs L-theanine within 30 minutes and that higher doses increase alpha wave production and relaxation.
(Source: Natural Health magazine, online at www.naturalhealthmag.com.)