Apparently, since the 1980s there has been trace amounts of morphine in the cheeses that we've been eating. On top of being regulated by Dairy Management to be placed in as much of our food as possible, it's got legitimate addicting properties. When cheese is processed, the levels of the morphine are greater than would be in just plain milk.
“Since cheese is processed to express out all the liquid, it’s an incredibly concentrated source of casomorphins—you might call it dairy crack.”
Read more at Care2 by clicking the dairy crack