Allegro argued that Jesus never existed as a historical figure but was rather a mythological creation of early Christians under the influence of psychoactive mushroom extracts such as psilocybin.

As Time magazine put it in an article headed "Jesus as mushroom":[3] To some biblical scholars in Britain, the new book looked like the psychedelic ravings of a hippie cultist.

[5] Mark Hall writes that Allegro suggested the Dead Sea scrolls all but proved that a historical Jesus never existed.

[6][clarification needed] Philip Jenkins writes that Allegro was an eccentric scholar who relied on texts that did not exist in quite the form he was citing them, and calls the Sacred Mushroom and the Cross "possibly the single most ludicrous book on Jesus scholarship by a qualified academic".

[8] In November 2009 The Sacred Mushroom and the Cross was reprinted in a 40th anniversary edition with a 30-page addendum by Prof. Carl A. P. Ruck of Boston University.