A contraceptive taken by mouth (see CONTRACEPTION). It comprises one or more synthetic female hormones, usually an oestrogen (see OESTROGENS), which blocks normal OVULATION, and a progestogen which influences the PITUITARY GLAND and thus overrides normal control of the woman's menstrual cycle (see MENSTRUATION). Progestogens also make the uterus less congenial for the fertilisation of an ovum by the sperm.