New knowledge in the physiology of hormonal contraceptives.

The present review addresses some of the new knowledge regarding the physiology and mechanisms of action of hormonal contraceptives. Specific topics that are discussed include oral contraceptives, intravaginal rings, long-term contraception, gonadotropin-releasing hormone agonists and antagonists, and antiprogestins. It has been shown that in combined oral contraceptives, lower doses of the new progestins (desogestrel, norgestimate, and gestodene) can be used to inhibit ovulation compared with norethindrone and levonorgestrel. In addition, lower doses of ethinyl estradiol are now used with progestins. Estrogen has been added to intravaginal rings containing levonorgestrel or norethindrone acetate to reduce frequency of bleeding. A new ring containing 3-keto-desogestrel is under evaluation. The use of subdermal implants containing levonorgestrel is currently a popular and highly effective method of long-term contraception. Studies show that gonadotropin-releasing hormone agonists and antagonists can provide ovarian suppression, and antiprogestins such as RU486 effectively block the midcycle gonadotropin surge. These and other novel methods of hormonal contraception are still years away from general use.