Diary of a Drug Fiend is widely thought to be based upon Crowley's own drug experiences, despite being written as a fiction. This seems almost conclusively confirmed by Crowley's statement in the novel's preface: "This is a true story. It has been rewritten only so far as was necessary to conceal personalities." Crowley's own recreational drug use and also his personal struggle with drug addiction, particularly heroin, is well documented. Crowley made a study of drugs and their effects upon the body and mind, experimenting widely himself. Many of his conclusions are present within this novel. Diary of a Drug Fiend encapsulates much of Crowley's core philosophy concerning Thelema and his conception of True Will.