When melatonin gets released at night, the hormone sends signals to your body that it’s time to start winding down. As a result, your body goes into “rest mode,” with a focus on repair and restoration—and daytime functions like digestion are essentially turned off. (That’s why experts say to avoid eating late at night if you can, as your metabolism naturally slows.) 

When you take melatonin, you kick-start this rest-and-recover process. So if you take the sleep aid, say, right after eating, you could impinge on your digestion without even knowing it. “If you eat your dinner late, let’s say 7:30 p.m., and then you take your melatonin at 8 p.m., you may be quieting your metabolism a little bit,” says Romm. “You may not get as much digestive fire, and it may actually affect weight gain.” 

Of course, there’s an easy fix: Just space out the time between eating and taking your melatonin! “If that means you need to bump your dinner a little earlier or take your melatonin a little later, that seems to be the antidote,” Romm adds.