According to Nature World News, those who suffer from insomnia or do not otherwise get a good night's sleep each night should stay away from caffeinated beverages, as they won't give you the energy you desire. Three nights in a row of inadequate sleep seems to be the limit to what some would call the magical restorative powers of a hot cup of coffee.
"These results are important because caffeine is a stimulant widely used to counteract performance decline following periods of restricted sleep," said Tracy Jill Doty, lead author of the study done by the American Academy of Sleep and Medicine.
Science World Report reported that the experiment consisted of 48 people who got only five hours of sleep for a total of five nights. Of those 48 people, half were given 200mg of caffeine each day while the other half were given a placebo. They were then tested on mood, sleepiness, wakefulness, and reaction time, along with spontaneous cognitive tests throughout their day.
In the first two days the group with the 200mg of caffeine had faster reaction times and better results, but by day 3 the caffeine had little to no effect.
"The data from this study suggests that the same effective daily dose of caffeine is not sufficient to prevent performance decline over multiple days of restricted sleep,"said Doty. "This is particularly important information for the military, where war fighters may have restricted sleep and may also be using caffeine."