The modern hormonal contraceptives fall into several major categories (Table 25.3), each with its own mechanism of contraceptive action. Individual compounds are discussed with the estrogens and progestins in the previous section.
Combination Tablets: Mechanism of Action. Although recognized in the early 1940s that either estrogens or progestins could inhibit ovulation, it was subsequently found that combinations were highly effective. Some problems, such as
TABLE 25.3 Comparison of Steroid Contraceptive Regimens
Products are available in 21- or 28-day dispensers and refills. The 28-day dispensers contain several inert (or Fe21-containing) tablets of a different color, taken daily after the 21 days of active tablets. Doses of active tablets are shown.
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