Nothing personal. Our additive kills the wolves, too... the shifters, and those disgusting little things that eat corpses. Anything with a taste for human. Except us. Mankind's a limited resource, after all.
Vamptonite is what Sam and Dean nickname the blood of humans who have been eating foods with the Leviathan's additive modified corn syrup in 7.22 There Will Be Blood. The modified sweetener produced by SucroCorp renders people lethargic and causes overeating. When eaten by or injected into vampires, it kills them almost instantly.
The tainted blood is not harmful to Leviathans, but Dick Roman plans that in addition to turning humanity into a well-fed docile food source, it will also eliminate other predators -- notably werewolves, ghouls, shapeshifters, anything with a taste for human flesh and blood.
- The term "vamptonite" is a play on the term kryptonite -- an ore from the planet Krypton which incapacitates Superman.