There is an ancient story of Mithridates of Pontus cultivating an immunity to poisons by regularly ingesting sub-lethal doses. (e.g. here, or here).
This strikes me as being extremely unlikely for many 'poisons' known in the modern world. Stuff like heavy-metal poisoning, or asbestos toxicity can accumulate for years with tiny doses, but would such be known in the ancient world, or recognised as a poison? Perhaps there is a nugget of truth for those poisons known in the ancient world.
So, my apologies for asking a two-part question, but I think the first half can be relatively simply answered 'yes' or 'no'.
- In general, will exposure to low-doses of a poison cause a resistance to the effects to build up (such that a lethal dose for a typical human would not be fatal for an individual)?
- Considering only poisons known in the ancient Mediterranean area, could there be any truth to the claim?