caffeine is a stimulant, and like all of them they have the potential to become addictive; making someone physically dependent on the drug itself. so right off the bat, i can say it is not "good" for your health. as per bad, well, stimulants cause neuron activity to spike, in which through longterm use can overuse the axons which is responsible for distributing the signals of neurons to others. when the synapse and terminals are becoming overused (especially through stimulants), they tend to lose their quality and perform at a lesser rate than before. thought process becomes slower, more prone to migranes/headaches, declines in memory retention and pattern recognition, too many negative characteristics to list. for comparison, running a CPU on higher clocking speeds than it normally runs (naturally, like base clock). eventually the circuits slow down and burn out, then the CPU gets fried. of course we are boilogical beings and these cells do have the capabilities to repair themselves. but the longer you do it, the harder it will be for these cells to repair themselves. lots of the time, people get to the point where the damage will become permanent. caffeine from coffee in moderate amounts is fine. but if you're taking caffeine pills, drinking tons of soda, coffee, and anything else that can be heavily potent in caffeine, then that's a different story.