Casein is mildly addictive and the reason many people crave cheese. During digestion, casein—a protein that is plentiful in cheese—gets broken down into casomorphins. These opioid-like peptides attach to dopamine receptors in the brain. This prompts the release of dopamine—a feel-good neurotransmitter linked to reward circuits. This causes your brain to associate casein (and cheese) with pleasure, resulting in cravings for more casein.