Mithridates VI, the King of Pontus (ancient Greek/Persian state located in modern day Turkey), had a paranoia that there were people who wanted to assassinate him through poison. This likely stemmed from his father being poisoned by his mother (reportedly), who favoured his brother over Mithridates as the heir to the throne. He noticed in his youth that the meals brought to him induced stomach pains. He connected the dots and deduced that his mother was trying to poison him slowly so that his brother would become the next king. He fled to the wilderness and devised a plan to protect himself. It is said that he began taking a concoction of various poisons in non-lethal doses every day, to develop an immunity to the most common poisons available during his time. This led to the idea of mithridatism – the gradual self-administration of non-lethal doses of poison to develop immunity. Ironically, Mithridates’ plan backfired eventually when he attempted suicide by poison after a massive defeat against Rome. He found that the poison had no effect on him and had to request his bodyguard to kill him by sword.
Mithridatism has been recorded or suspected in various times of history. Indian epics tell the story of the king Chandragupta Maurya – the first king to unite India – who selected a group of beautiful girls and raised them in the palace. He gave the order to administer small amounts of poison to these girls as they grew up, making them invulnerable to toxins. He called these girls vishakanyas (poison maiden) and believed that they could be used as assassins who could kill men through the act of sex.
There are suggestions that Rasputin was also a practitioner of mithridatism and that this was why he survived an assassination attempt involving poison, but there is not much evidence for this.
The practice of mithridatism is also mentioned in various fictions, such as The Count of Monte Cristo and The Princess Bride.
The concept of taking small doses of something to build up an immunity is still used in modern medicine. Desensitisation therapy is used to treat certain allergies, by exposing the body to small doses of the allergen. It is well-known that alcoholics and drug addicts required more substance to achieve the same effect as most people because they develop tolerance to it. There is some evidence that mithridatism is an effective way to build immunity to venomous snake bites.
However, not all poisonings can be avoided with mithridatism. Poisons such as cyanide pass through the system too quickly to create any tolerance, while heavy metals simply build up in the body to create a toxic effect after a history of exposure.