I thought Head was rated R, which was one of the reasons why it didn't do so well: none of the Monkees' young fans could see it. That, and the fact that it was an acid trip of a movie (literally).
http://www.imdb.com/title/tt0063049/
G, as noted on IMDB (and the video).
It was based on acid trip musings of Jack Nicholson.
Only 33 Revolutions Per Monkee did more to alienate Monkees fans from the band (although booking the Jimi Hendrix Experience as tour opener probably also went over their heads).