Primal therapy became very influential during a brief period in the early 1970s, after the publication of Janov's first book, "The Primal Scream". It inspired hundreds of spin-off clinics worldwide and served as an inspiration for many popular cultural icons. Singer-songwriter John Lennon, actor James Earl Jones, and pianist Roger Williams were prominent advocates of primal therapy. Primal therapy has since declined in popularity, partly because Janov had not demonstrated in research the outcomes necessary to convince research-oriented psychotherapists of its effectiveness. Proponents of the methodology continue to advocate and practice the therapy or variations of it.