<prompt> All of the following mechanisms of action of oral contraceptive pills are true, except:Inhibition of ovulationPrevention of fertilizationInterference with implantation of fertilized ovumInterference with placental functioning  <response>: Ans. is d, i.e. Interference with placental functioningRef: KDT 6thed, p314-315Even if the mechanisms by which OCPs act is not known to us, by sheer common sense we know that Interference with placental functioning is the incorrect option as if placenta is formed it means pregnancy is occurring which in itself is incorrect with regard to OCPs as OCPs are used to prevent conception.The mechanism of action of OCPs in brief: Main mechanism of action of combined pills is - prevention of ovulation. Combined pills act by decreasing both LH and FSH They do not interfere with placental functioning. When taken daily for 3 out of 4 weeks, they provide virtually absolute protection against conception. 