Ans-BREF: William's 22nd ed chapter 32PROGESTERONE ONLY PILLS: So-called mini-pills are oral progestin-only contraceptives that are taken daily. Unlike combined oral contraceptives, they do not reliably inhibit ovulation. Rather, their effectiveness depends more on alterations in cervical mucus and effects on the endometrium.Because the mucus changes do not last longer than 24 hours, mini-pills should be taken at the same time every day to be maximally effective.These contraceptives have not achieved widespread popularity because of a much higher incidence of irregular bleeding and a somewhat higher pregnancy rate than combined contraceptivesBenefitsProgestin-only pills have minimal if any effect on carbohydrate metabolism or coagulation, and they do not cause or exacerbate hypertension.They may be ideal for some women who are at increased risk of cardiovascular complications. This includes women with a history of thrombosis, hypertension, or migraine headaches, or who are older than 35 years of age and who smoke.The mini-pills is often an excellent choice for lactating women. In combination with breastfeeding, it is virtually 100 percent effective for up to 6 months and does not impair milk productionDisadvantagesThe major drawback of progestin-only pills is a contraceptive failure. With these failures, there is a relative increase in the proportion of ectopic pregnancies.Irregular uterine bleeding is most common and another distinct disadvantage and may manifest as amenorrhea, spotting, breakthrough bleeding, or prolonged periods of amenorrhea or menorrhagia.Functional ovarian cysts develop with a greater frequency in women using these agents, although they do not usually necessitate intervention.A distinct disadvantage is that these contraceptives must be taken at the same or nearly the same time dailyFinally, unlike combined oral contraceptives, the mini-pills does not improve acne and may even worsen it in some women. Contraindications:Progestin-only pills are contraindicated in women with unexplained uterine bleeding, especially in older women.