hard drug vs soporific

hard drug

noun

  • An illegal, highly-addictive drug. 

soporific

noun

  • Something inducing sleep, especially a drug. 

  • Something boring or dull. 

adj

  • Boring, dull. 

  • Tending to induce sleep. 

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