Tolerance to toxins/posions

A while ago I was reading “The Count of Monte Cristo” and one of the plot points of the book invovles a character building up a tolerance to posion by imbibing very slight amounts and slowly up the dosage as to develop a sort of “immunity”(or at least, the ability to survive what would kill most people).

My question is: Is that possible? Would that idea work in practice?

Build up an immunity to poison?

Wasn’t Rasputin supposed to have had a huge tolerance for arsenic?

Rasputin was supposed to have huge tolerance for everything. Including bullets.

That would be useful, but sounds like a pain in the ass to build one up :smiley: