At least an R rating for much nudity.

Counterpoint: The female lead is nude briefly while crumpled in a shower after passing out early in the movie, and then part of one breast, including the nipple, is visible for several seconds while she lies in bed asleep. Later, her unclothed backside is momentarily visible as the camera recedes from a scene of a man and woman commencing to make love. Other than that the male removes his shirt a couple seconds before this, no other nudity appears in the movie.