Prudence and the Pill gained minor notoriety in 1968 as the first film comedy dealing with the new birth-control pill. David Niven substitutes aspirin for his wife's (Deborah Kerr) birth control medicine, hoping that she will become pregnant by her lover (Keith Mitchell) -- thereby freeing him to dally with his mistress (Irina Demich). Meanwhile, Niven's niece (Judy Geeson) does a switch job on her parents' pills, hoping that once her mom is pregnant, Geeson will be left alone to pursue her own love life. How did such prominent actors as Niven, Kerr, Robert Coote and Dame Edith Evans get mixed up in this high-gloss sleaze? Prudence and the Pill was not only unfunny, but was rendered anachronistic within a year of its release.
~ Hal Erickson, All Movie Guide