(a) The contraceptive pills contain little amounts of hormones like progesterone or a combination of progesterone and oestrogen. They act bringing about the inhibition of ovulation and implantation. They also act by altering the quality of cervical mucus to prevent or ** entry of sperms.
(b) These pills have to be taken regularly for 21 days starting with the first four days of menstruation, to be repeated after a gap of seven day
