Researchers in Japan have discovered an amino acid in green tea which acts as a relaxant without causing drowsiness. From the October issue of Life Extension magazine:
The tranquilizing effects of theanine are not imaginary. Theanine readily crosses the blood-brain barrier of humans and exerts subtle changes in biochemistry. An increase in alpha waves has been documented, and the effect has been compared to getting a massage or taking a hot bath. Theanine is different than kava-kava in that it doesn't cause drowsiness. And unlike tranquilizing drugs, it doesn't interfere with the ability to think. Studies on rodents show just the opposite: theanine enhances the ability to learn and remember. By shutting down the "worry" mode, theanine increases concentration and focuses thought. This is the concept behind the Japanese tea ceremony which causes a person to focus on the moment. Consider this: the risk of mortality for Japanese women who practice tea ceremony is half of other Japanese women. The Japanese are already the longest-lived people on earth.Theanine is a caffeine antagonist. It does the opposite. Th effects can readily be seen in EEGs of rodents given caffeine, then theanine. One of the things that theanine changes is GABA, a brain chemical known for its calming effect. Theanine increases GABA, while caffeine decreases it. GABA doesn't just relax, it also creates a sense of well-being. Theanine's ability to increase this brain chemical can put you in a better mood by changing biochemistry. Theanine also increases levels of dopamine, another brain chemical with mood-enhancing effects.