Co-writer Jack Nicholson actually compiled the film's soundtrack in its final form, with snippets of the film's dialogue between songs, and is so credited on its LP album cover (when he saw Michael Nesmith at work in the studio and asked if he could help, Nesmith let him take over, because he said "I just want to go home."). Nicholson had unwavering enthusiasm for the film, joining in a stickering campaign to promote its premiere and declaring later that "I saw it, like, 158,000,000 times, man. I loved it!"
In one scene, a desert wanderer faces off against an uncooperative soda machine as a jingle plays. Coca-Cola reportedly was not amused and tried to get an injunction against the scene. When the film reappeared on cable and home video in 1986, Coca-Cola owned Columbia Pictures, and the matter was apparently forgotten.
Rumors abound that the film's title was chosen in case a sequel was made. The advertisements and tagline for said sequel would supposedly have been "From the people who gave you HEAD".
Victor Mature agreed to appear in the film after reading the script, admitting none of it made sense to him: "All I know is it makes me laugh." His character, "The Big Victor", is presumed to be a comic jab at RCA Victor, which were the distributors for The Monkees' records, and whose parent company also owned NBC, which aired their TV series.
Michael Nesmith's birthday party sequence was shot at Paramount Pictures on a set from Rosemary's Baby (1968). It featured 100 extras and pop artist Edward Kienholz, whose 1964 sculpture "Back Seat Dodge '38" was featured on-set.
Mireille Machu: the girl who plays Lady Pleasure and kisses all four of The Monkees near the beginning of the film was Jack Nicholson's girlfriend at the time.
John Brockman: the man whose head was used for the infamous ad campaign upon the film's 1968 release can be seen in it exactly 78 minutes in, in much the same pose.