[Telepathic Intruder]

Mithradates, known as the poison king, ingested poisons in small amounts for most of his life and was virtually immune to every known form of them in his time. He must have had some interesting antibodies.

[Pearls Before Swine]

Mithradates, known as the poison king, ingested poisons in small amounts for most of his life and was virtually immune to every known form of them in his time.

It's a nice story, but it might not be beneficial with cumulative poisons (arsenic, heavy metals).