What is "drug of choice"

n. 1 (context legal narcotics English) The particular (usually illicit) substance that a suspect is addicted to. 2 The best-choice medication to treat a particular medical problem.

Drug of Choice is a novel written by Michael Crichton under the pseudonym John Lange. It was originally published in 1970. Hard Case Crime republished the novel under Crichton's name in November 2013.