Progestogen-only contraceptives (POCs) may be more suitable than combined hormonal contraceptives for women with diabetes, those who are breastfeeding, women with a history of thromboembolism, older women (over 35, especially smokers), hypertensives or those who develop transient hypertension on combined contraceptives and when oestrogens are contraindicated. Their disadvantage, compared to combined contraceptives, is the higher incidence of irregular bleeding, a higher rate of ectopic pregnancy and a slightly lower contraceptive efficacy.
The mechanism of action of traditional POCs relates to premature endometrial secretory patterns, cervical mucus thickening and hostility to sperm and tubal transport disruption. Ovulation is inhibited in about half of the cycles and contributes only partly to the contraceptive efficacy. In contrast to traditional POCs, the contraceptive efficacy of the progestogen desogestrel is achieved primarily by suppression of ovulation and its high contraceptive efficacy and low incidence of ectopic pregnancies is comparable to that of combined contraceptives. In addition, desogestrel possesses low androgenic activity so it has no clinically significant effects on carbohydrate or lipid metabolism.
Pill taking The first packet is started on Days 1—5 of the cycle and a tablet is taken daily without a break even through the period. If started after this time, additional contraception is needed for 2 days. Additional contraception is required for the first seven days of the first course of Noriday.
Missed pills It is important that the pill is taken at the same time each day because contraceptive efficiency falls markedly if tablets are taken late or omitted. The best time to take them is several hours before the usual time of intercourse so that the blood levels are high. A POC is regarded as 'missed' if taken only three hours late (12 hours with desogestrel). In such cases, the missed pill should be taken immediately and normal pill taking resumed when the next dose is due. Extra precautions must be taken for seven days.
Changing from a combined contraceptive to a POC POCs are started without a break on the day following the last active combined contraceptive tablet or on the day of removal of vaginal ring or transdermal patch. No additional contraception is necessary. The start may be delayed with desogestrel up to the day following the usual tablet-free, patch-free, ring-free or placebo interval but additional contraception is necessary for seven days.
Starting POC after pregnancy There is no evidence to suggest that POCs have a detrimental effect on breast milk or infant growth. POCs may be started up to and including 21 days post partum without the need for additional contraception. If started later than 21 days, pregnancy should be excluded and additional contraception used for seven days.