For the study, researchers had 48 adults sleep only five hours for five nights in a row. During the day, half of the participants were given two 200-mg doses of caffeine, while the rest were given a placebo. The researchers tested each participants' performance, including their mood, energy, and cognition each day. After three days, they found that the doses of caffeine lost their effect on the participants.In other words, after three days, the test subjects were so sleep-deprived that the caffeine's once-powerful boost wasn't enough to bolster performance.Related: Are You Sleeping More or Less Than The Average College Student? So, grabbing a cold brew after several sleepless nights probably won't make much of a difference. The best remedy for sleep-deprivation is, you guessed it, sleep. If your problem is falling asleep in the first place, give this super-simple trick a try.Related: 4 Healthy Caffeine Fixes — No Coffee Or Soda Required