Chocolate doesn't have much caffeine, but it does have theobromine ("food of the gods", for the classicists), which is also a methylxanthine like caffeine and like theophylline ("leaf of the gods", also used as an asthma medicine, though it has fallen out of favor recently), which is the main methylxanthine in tea. Methylxanthines increase the intracellular concentration of cyclic-AMP, which regulates a number of cellular processes. (Don't ask me which ones, my last biochemistry course was in 1974.)

Drinking caffeinated beverages does make you thirsty, because caffeine is also a diuretic. That is, it increases urine output (if you're interested I can tell you how) and, if the concentration is high enough, you can end up losing more water than you take in. (Alcohol does the same thing: remember Archie Bunker's line, "You don't buy beer, you only rent it.")

I recently attended a lecture by a gastroenterologist on GERD (gastro-esophageal reflux disease), which has become the disease-of-the-month in some circles. I asked him if caffeinated beverages like Coke caused increased reflux and heartburn. Turns out that it's not the caffeine, it's the carbonation: the gas in the drinks causes your stomach to dilate quickly, and that is a strong stimulus for reflux.

I would strongly concur with the first part of Colwyn's post at the top of this thread: most of us don't drink nearly enough water. I tell my overweight pediatric patients that they should drink a glass of water BEFORE each meal, so they eat less. Many people think they're hungry when they're actually thirsty. However, it's also true that tap water in many areas is both vile-tasting and toxic. And many of the bottled waters now for sale are not very "pure" ripoffs. I think Brita filters make sense.

Now me, I'm partial to Moxie, which I discovered in Maine. In addition to the usual bad stuff, it has the flavoring ingredient of Angostura bitters. Yum!

Aloha,
Mark