ABSTRACT
Mechanism of action Aside from secondary contraceptive effects on the cervical mucus and to impede implantation, 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, the endometrium. So the withdrawal bleeding has minimal medical significance, can be deliberately postponed or made infrequent as in tricycling (see below), 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).
