There is a limited amount of time for caffeine to improve your sleepiness.
When you thought coffee would help but you’re still annoyed by everyone pic.twitter.com/nmepIIDfMh
— Leo Abdala (@FactsOfSchool) August 16, 2016
A lot of us drink coffee because we want that caffeine boost that sharpens our wit just enough to get through our day. If you are too sleep deprived, no matter how much coffee you drink, you will still feel tired.
After 3 days of sleep restriction, caffeine did not improve the participants alertness.