By now the most thoroughly studied beverage in the world, coffee is not known to cause heart disease or to promote any kind of cancer or stomach ulcers. It can cause coffee nerves and jitters if you drink too much of it. Most people like the brief lift that caffeine provides, and it is not known to be harmful for healthy people. But if you decide to stop drinking caffeinated coffee, do so gradually to avoid the headache that caffeine withdrawal temporaily causes.
(Source: UC Berkeley Wellness Letter: Healthy Eating)