ABSTRACT
The mechanism of action is complex because of variable interactions between the administered progestogen and the endogenous activity of the woman’s ovary. With regard to effect of body mass, studies are suggestive, but not conclusive, that the failure rate of old-type progestogen-only Pills (POP) may be higher with increasing weight, as was well established in early studies of progestogen rings and some implants. Pending more data, a logical policy now is to make the Desogestrel POP one’s first choice for women weighing more than 70 kg, especially if they are young. However, because of reduced fertility, there can be little doubt that one old-type POP daily will be adequately effective in older overweight women, in women older than 45 years, or during established breastfeeding. Beware – unwanted conceptions are common when lactating POP users have not been adequately warned that their margin for error in POP taking will diminish at weaning.
