Beyond that, though, researchers are still developing a concrete explanation for why the munchies happen. And, of course, most of this research has been done in non-human animals. So we don't know for sure how much of it is applicable to humans — but researchers are on the case.
Taking all of this together, it seems like marijuana may make us hungrier by working on a few different levels: It increases our appetite, it makes already-good food even more appetizing, and it makes food taste better when we get it. So, basically, just remember to order the pizza before you light up.