Current progestin-only methods include Depo-Provera, progestin-only pills and intrauterine devices impregnated with progestin. A new etonorgestrel implant system awaits final approval from the FDA.

Mechanism of action: Progestin-only methods have many documented mechanisms of action, including inhibition of ovulation, thickened and decreased cervical mucus, suppression of mid-cycle peaks of LH and FSH, inhibition of progesterone receptor synthesis, reduction in the number and size of endometrial glands, reduction in ciliary activity within the fallopian tube, and premature luteolysis (decreased functioning of the corpus luteum) (83-86). Progestins at high concentrations likely suppress the initiation of folliculogenesis at the level of the hypothalamus. At slightly lower concentrations folliculogenesis can be initiated but the progestin prevents the LH surge at the level of the pituitary and therefore prevents ovulation. At even lower concentrations, progestins alter cervical mucus, tubal motility and/or the endometrium (87).

Advantages: Progestin-only methods do not have an estrogen component, thereby decreasing the complications attributable to estrogen (such as thrombophlebitis, cardiovascular disease and pulmonary embolism). Specific non-contraceptive benefits of these methods include scanty or no menses, decreased menstrual cramps and pain, suppression of pain associated with ovulation, decrease in endometrial cancer, ovarian cancer, and pelvic inflammatory disease, and potential improvement of the pain associated with endometriosis. All progestin-only contraceptive methods are reversible. Non-parental administration of progestin provides long term, effective contraception, decreases the risk of ectopic pregnancy, and is not coitally dependent. Specific indications for these methods may include women who are breastfeeding, women who are at greater risk for thromboembolic events, and women who cannot take estrogen.

Disadvantages: These methods do not protect against sexually transmitted disease and HIV and can alter the menstrual cycle (including breakthrough bleeding with an increased number of days of light bleeding, and potential amenorrhea).

The contraindications to progestin-only contraceptives are listed in Table 7. The only absolute contraindications methods include pregnancy, unexplained abnormal vaginal bleeding suspicious for a serious underlying condition, or breast cancer. Active liver disease has been deleted from the list of contraindications to DMPA. In general, on should exercise care when using this method in women with acute, severe liver disease or liver tumors.