It would seem that the resolution to the caffeine debate, at least in terms of short-term effects, is simple moderation. Drunk to excess, coffee literally verges on poison; drunk in moderation, it is still the beloved tonic of tradition, a gentle aid to thought, labor, and conversation.
But just how much is enough and how much is too much? No study will commit itself. One can estimate based on inference. Few, if any, studies report negative effects from doses of caffeine under 300 milligrams a day. Since the average cup of coffee (or single serving of espresso) contains about 100 milligrams of caffeine, one could infer from this evidence that anyone should be able to drink about three cups of coffee a day and enjoy the benefits of caffeine with none of the drawbacks. Such a figure assumes, of course, that you do not also consume quantities of cola drinks, chocolate bars, and headache pills. This is a conservative estimate, however. One could infer from other studies that five cups a day is safe for most people. Furthermore, reaction to caffeine varies greatly from individual to individual; some people cannot consume any amount comfortably.