Cheese contains a chemical found in addictive drugs, scientists have found. The team behind the study set out to pin-point why certain foods are more addictive than others. Using the Yale Food Addiction Scale, designed to measure a person’s dependence on, scientists found that cheese is particularly potent because it contains casein. The substance, which is present in all dairy products, can trigger the brain’s opioid receptors which are linked to addiction.Your body contains these receptors in the brain, spinal cord, and digestive system. Opioids have many side effects, including pain relief and euphoria, which alone can be addictive (who doesn't like being happy and pain-free?), but they also can directly cause addiction through molecular changes in the brain and involvement of naturally occurring (aka: endogenous) opioids in the human body - chemicals like endorphins, dynorphins, and endomorphin. These chemicals can affect the release of other chemicals in the brain, which can results in behavioral impacts (such as causing drug-seeking behavior).
Obviously, cheese addiction isn't as severe as addiction to other opioids (such as, say, cocaine or morphine), or else we'd hear about a lot more cheese addiction treatment programs.