And like Confused said, it can cause heartburn and other digestive problems. My father-in-law ended up in hospital with bleeding ulcers from too much coffee.

Try tea instead. Tetley has a very nice tasting herbal tea called Vitality with hibiscus, lemongrass, orange, gingko (for your brain), blueberries, and ginseng and other ingredients. Ginseng is a natural adaptogen. It gives your body what it needs, no matter what it needs. The Chinese have used it for 5000 years. American ginseng and Siberian ginseng are not true ginsengs, although they can be useful. Korean red or white are "real" ginseng, and the white is less strong than the rest. The only reason I mention the Tetley is because I was pleased at how good it tastes. Any Chinese or Korean ginseng tea will give you a boost when you need it, and calm you down when you don't need it. Ginseng helps your body adapt to stress.

If you want caffeine, try black tea or even green tea. They're not as addictive and not as hard on the stomach as coffee.

And as a caveat, whatever you choose to drink, don't go to extremes. Two or three cups a day is plenty.