opium vs tranquilizer

opium

noun
  • Anything that numbs or stupefies. 

  • A yellow-brown, addictive narcotic drug obtained from the dried juice of unripe pods of the opium poppy, Papaver somniferum, and containing alkaloids such as morphine, codeine, and papaverine. 

tranquilizer

noun
  • That which tranquillizes or soothes. 

  • A drug used to reduce anxiety or tension. 

How often have the words opium and tranquilizer occurred in a corpus of books? (source: Google Ngram Viewer )