ABSTRACT
COMBINED ORAL CONTRACEPTIVES Mechanism of action Aside from secondary contraceptive effects on the cervical mucus and to impede implantation, combined oral contraceptives (COCs) primarily prevent ovulation. They therefore remove the normal menstrual cyle and replace it with a cycle which is user-produced and based only on the end organ, i.e. the endometrium. So the withdrawal bleeding has minimal medical significance, can be deliberately postponed or made infrequent (e.g. tricycling, see p. 58), and if it fails to occur, once pregnancy is excluded, poses no problem. The pill-free time is the contraception-deficient time, which has great relevance to maintenance of the COC’s efficacy (see below).
