The Collaborative International Dictionary of English v.0.48:

Mithridate \Mith"ri*date\, n. (Med.)
   An antidote against poison, or a composition in form of an
   electuary, supposed to serve either as a remedy or a
   preservative against poison; an alexipharmic; -- so called
   from King Mithridates, its reputed inventor.
   [1913 Webster]

         [Love is] a drop of the true elixir; no mithridate so
         effectual against the infection of vice. --Southey.
   [1913 Webster]