Adrienne Mayor, “Mithridates of Pontus and His Universal Antidote,” in Toxicology in Antiquity (2nd ed.), 2019, 161-174.
Mithridates hypothesized that tiny doses of poisons could be ingested over time in carefully increasing amounts and thus ultimately make the body capable of tolerating larger doses that would normally be fatal – a dose-dependent protective mechanism, akin to modern vaccines. (He was right, about some chemicals at least – we call it hormesis, if you’re keen to learn more.)
Mithridates’ recipe for his inoculating toxin brew reportedly contained tons of things, from herbs to toxic skink skin to blood from a breed of poisonous ducks. It most likely also contained St. John’s Wort (hypericum). Mayor writes:
“Molecular scientists have recently discovered hypericum’s remarkable antidote effect, not yet completely understood. The herb activates the liver to produce a potent enzyme that is capable of neutralizing a great many potentially dangerous chemicals—as well as prescribed drugs for various conditions.”
Well, Mithridates lived into his 70s in an age when the life expectancy was around 45, surviving numerous assassination attempts, taking his toxin brew daily, and thriving, by all accounts — at least until he commited suicide in 63 BCE.