L-theanine, a unique amino acid, accounts for over 50% of the free amino acids in tea leaves and less than 2% of the total weight of dry leaf in both black and green teas. Studies show that L-theanine may promote relaxation and calm by influencing particular chemicals in the brain. Japanese researchers discovered that L-theanine is derivative of glutamic acid, a neurotransmitter located in the brain. Easily absorbed by the brain, it influences chemicals such as dopamine and serotonin, which affect mood. Studies show that the amino acid, without causing drowsiness, enhances overall concentration and focus. The effect of L-theanine in combination with caffeine may contribute to the feeling of increased energy and overall calm that many tea drinkers experience.