User blog comment:Miskos3/Fairy Tail Chapter 486: The Fourth Guest, Review/@comment-7418318-20160525151848/@comment-5303512-20160526093050

Well Gajeel was able to slowly resist the poison of Torafusa, even fused the carbon into his iron! Freaking taking poison as an advantage!

But in all seriousness, I doubt a man made out of iron can really be Posioned unlike other beings who were mostly organic while Gajeel turns his external and internal parts iron. It's kinda like saying machines can be poisoned by organic anomalies.

Except for Freed who seems to be able to have some sort of tolerance level to the MBP.