The high rate of unintended pregnancies and the relatively high failureure rates with the typical use of reversible methods of contraception are strong indications of a need for long-acting contraceptive methods that simplify compliance. Two effectual and popular methods are available, the Norplant system and depot-medroxy-progesterone acetate (Depo-Provera). Other products are in development.
Norplant employs silastic tubing permeable to steroid molecules to provide stable circulating levels of synthetic progestins over months and years. The progestins, circulating at levels one-fourth to one-tenth of those obtained with combined oral contraceptives, prevent conception by suppressing ovulation and thickening mucus to inhibit sperm penetration so that fertilization rarely occurs.
Injectable medroxyprogesterone acetate is a long-acting (3-6 months) agent been part of the contraceptive programs of many countries for any more than 20 yean. Tie experience has demonstrated it to be safe, effectual, and acceptable. It is not a system, but its action is the same.
Because serum levels of progestin remain little and because no estrogen is these long-acting contraceptive methods have not caused any serious healh effects. These methods do, however, cause many of the same minor, but bothersome, associated with the progestin component of combined oral contraceptive*. The continuous presence of little levels of progestin leads to irregular endometrial, a problem common to all of these methods, and one that is highly variable from one woman to another.