If you haven’t been getting enough sleep, chances are good that your first move in the morning is to guzzle down a cup of coffee for some much-needed energy. However, data from new research indicates caffeine won’t help you wake up if you’re severely sleep-deprived or consistently getting less than a full night of rest. The researchers, who will present their findings this week at a conference in Denver, CO, concluded that a cup of coffee might help you look alive the morning after a single all-nighter, but regularly relying on caffeine to perk up after sleep deprivation will likely leave you more annoyed and irritable than you would be otherwise, and your ability to perform at the office will suffer. 

In this double-blind randomized study, 48 participants got five hours of sleep for five nights in a row, and every morning, they were either given 200 milligrams of caffeine, about the same caffeine content as a cup of coffee, or a placebo instead. All participants then attempted a cognitive task to simulate a day at the office, and although the participants who had caffeine did better than those who didn’t on the first two days, on the last three days, the caffeinated participants’ performance suffered. Plus, according to the research abstract, “those in the caffeine group rated themselves more annoyed than those in the placebo group” at the end of the sleep deprivation.

“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,” Tracy Jill Doty, a researcher at Walter Reed Army Institute of Research and the lead author of this study, explained in a press release.

TL;DR drinking all the caffeine if the world won’t be enough to save you from your bad sleep habits, and if you really want to make the most of your morning coffee, be sure to get a full night of sleep, too.