placebo vs prophylactic

placebo

noun
  • A dummy medicine containing no active ingredients; an inert treatment. 

  • The vespers sung in the office for the dead. 

prophylactic

noun
  • A medicine which preserves or defends against disease; a preventive. 

  • Any device or mechanism intended to prevent harmful consequences. 

  • A prophylactic condom. 

adj
  • Serving to prevent or protect against an undesired effect, especially disease or pregnancy 

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