Recent research suggests that those who use their cellphones past 9 pm suffer for it the next day.

There’s a good chance that if you’re checking your work emails late into the night, you get less done the next day, according to a pair of recent studies.

Research from Michigan State University found that specifically using a smartphone past 9 p.m. for work purposes caused people to be more tired and less engaged at work the following day–essentially, a hangover.

For one study, 82 upper-level managers completed daily surveys about their work and sleep habits for two weeks. The second study surveyed 161 participants, from a range of fields from manufacturing to dentistry.

“The nighttime use of smartphones appears to have both psychological and physiological effects on people’s ability to sleep and on sleep’s essential recovery functions,” Michigan State University Assistant Professor of Management Russell Johnson said in a news release.

Johnson, who co-authored the studies, is referring to the psychological toll of keeping your brain mentally engaged late into the night as well as the physiological effects that a smartphone’s “blue light” has on your body. Blue light suppresses your secretion of melatonin, a chemical that helps promote sleep.

For better sleep, Inc.’s Jeff Haden has suggested setting a cutoff time and sticking to it every night. But that’s easier said than done, especially when you have a never ending to-do list. The solution?

“Write down what you need to do first thing tomorrow,” Haden said. “You’ll rest easier knowing you have a plan to take care of what didn’t get done today.”