From the FAQ: "Most studies done on the l-theanine-caffeine combination have a l-theanine to caffeine ratio that isn't consistent with ratios you would expect

From the FAQ: "Most studies done on the l-theanine-caffeine combination have a l-theanine to caffeine ratio that isn't consistent with ratios you would expect from most teas. The studies used about twice as much l-theanine as caffeine by weight. The ratio found in most teas is reversed, with the possible exception of high quality green tea. Tea also increases fluoride intake which may lead to skeletal or other health problems when consumed in excess." I'd just like to put in a word for good deep-steamed sencha (fukamushi-cha), and for special occasions the more expensive gyokuro. Brew it properly and it's very, very delicious, and the effects are just lovely. You easily get four brewings from one dose of tea leaves. I drink it most days at work and it's such a delight!