John Belushi was offered a role in this film numerous times, but he originally turned it down. He eventually accepted the role, but died shortly afterwards. The producers were excited of having him on the poster wearing a diaper, even though no such scene appeared in the script. This was in the period Penny Marshall was supposed to direct based on a screenplay by John Hughes.
Martha Coolidge had a dispute with the studio in the editing room. As a first-time filmmaker, she shot several scenes with gratuitous nudity, but chose to keep them out of the film during the cutting process. The studio disagreed and eventually fired her. Coolidge decided not to request an Alan Smithee credit, though she has said in interviews that she sometimes regrets that decision.
In the mid 1970s, Paramount Pictures paid a great amount of money to secure the rights to Alex Comfort's sex manual The Joy of Sex, just so they could use the title, which they found to be highly commercial. In 1978, they hired Charles Grodin to write a script, telling him the movie "could be about anything". Grodin decided to use this exact situation as the premise: a Hollywood writer struggles to write a script based on a sex manual after a big studio acquires the rights. When he finished his first draft, Paramount passed. Grodin finally managed to get his screenplay green lit by MGM as Movers & Shakers (1985). Note that in that movie, the sex manual is called "Joy In Sex".
John Hughes wrote an early version of the script which consisted of several unrelated vignettes. Penny Marshall was offered to direct this version in early 1982.
P.J. Soles was originally cast in the film, but production was delayed, due to the death of John Belushi. When production resumed, Soles was replaced.