Report: Starbucks coffee has twice the caffeine

So says the Wall St. Journal. The article goes on to say (emphasis mine):

The more robust taste certainly lures many consumers. But in light of mounting research on how the body reacts to higher caffeine, the stronger brew suggests another reason coffeehouses have resurrected a beverage that once had considerably less buzz in the U.S. However accidentally, their business may be thriving in part because customers are habituated to a drug, albeit one legal and relatively harmless.

For caffeine, scientists usually use the term "physically dependent" rather than "addicted," a term they reserve for severe cases, as in a hooked heroin user or someone who smokes a few packs of cigarettes a day. But in recent years researchers have quantified specific doses of caffeine and linked them with withdrawal symptoms including headache, drowsiness and difficulty concentrating.

These ill effects are important. Recent research has shown people often choose to maintain their caffeine intake more to avoid the irritable results when they don't get it, than for the positive effects when they do. Caffeine withdrawal usually begins within 12 to 24 hours after the last coffee was drunk, which may neatly explain why people often reach for their mug first thing in the morning.

"You wake up in a state of withdrawal," says Laura Juliano, an assistant professor of psychology at American University who has studied caffeine.