Sure, a few minutes ago you might have said you were too full to eat another bite, but a few drags from a joint later and those gooey bites of salty goodness are hitting the spot like no other snack has before.

A case of the munchies is no figment of the imagination — decades of research have found that both casual and heavy marijuana users tend to overeat when they smoke.

But what is it about weed that makes us want to snack?

Marijuana may effectively flip a circuit in the brain that is normally responsible for quelling the appetite, triggering us to eat instead, according to a new study in mice published in the journal Nature Neuroscience.

It all comes down to a special group of cells in the brain which normally get activated, or switched on, after we've eaten a big meal to tell us we've had enough. In the brain, though, the psychoactive ingredient in weed appears to activate just one component of those appetite-suppressing cells, known as pro-opiomelanocortin (POMC) neurons, making us hungry instead.