The mini-pill contains a small amount of progestin hormone. As with the combination pill, it must be taken every day, ideally at approximately the same time. The mini-pill works by thickening the cervical mucus and making the uterine lining unfavorable for implantation of a fertilized egg. About half of the women who use the mini-pill ovulate, but they do not become pregnant because sperm become trapped in the thickened cervical mucus, unable to find the egg.

The mini-pill is ideal for women older than 40 who may not ovulate on a regular basis, and for women who are exclusively breast-feeding their infant. It is not recommended, however, for women who have had pregnancy-related gestational diabetes. This is because women who have had gestational diabetes are more likely to develop diabetes as older adults. The progestin-only pill may increase the likelihood that diabetes will develop in such women.

The mini-pill is also a good choice for women who cannot tolerate estrogen and for women who smoke but want to use a hormonal method of birth control.

In general, the ability to become pregnant resumes quickly after discontinuing the mini-pill as compared to women who discontinue using the combination pill. Although menstrual-like bleeding appears within a week of stopping either pill, menstrual-cycle length may not return to normal until the second or third month after stopping the pill.

The mini-pill does not appear to increase the risk of breast cancer.

The most common reason women discontinue the mini-pill is irregular menstrual bleeding including skipped periods or no bleeding, unpredictable spotting, irregular bleeding, and sometimes heavier and prolonged bleeding.