5.5.4 Disadvantages of mini-pills
For women who are not breastfeeding, the most common side-effects are: changes in menstrual bleeding including irregular periods, spotting or bleeding between periods (which is common), and amenorrhoea or missed periods (which is less common, but may continue for several months). Note that some women see amenorrhoea as an advantage. A few women may have prolonged or heavy menstrual bleeding.
Breastfeeding women normally do not have regular periods for some months, whether or not they are using progestin-only oral contraceptives. Therefore, menstrual changes due to progestin-only oral contraceptives generally are not noticed or bothersome. Progestin-only oral contraceptives may lengthen amenorrhoea during breastfeeding. For women who are not breastfeeding, even taking a pill more than a few hours late can increase the risk of pregnancy, and missing two or more pills increases the risk greatly.