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Oral contraceptives come in a variety of formulations. The main division is between combined oral contraceptive pills, containing both synthetic estrogens and progestogens (progestins), and progestogen only pills (mini-pills). Combined oral contraceptive pills also come in varying types, including varying doses of estrogen, and whether the dose of estrogen or progestogen changes from week to week. == Mechanism of action == Combination pills usually work by preventing a person's ovaries from releasing eggs (ovulation). They also thicken the cervical mucus, which keeps sperm from joining with an egg. The hormones in combination and progestogen-only pills also thin the lining of the uterus. This could prevent pregnancy by interfering with implantation of a blastocyst. Main action in typical use is prevention of ovulation. ==Combined oral contraceptive pills== All contain an estrogen, ethinyl estradiol or mestranol, in varying amounts, and one of a number of different progestogens. (Regarding the estrogen, the inactive 3-methyl ether of ethinyl estradiol, which must be metabolized by the liver into the active ethinyl estradiol; 50 µg of mestranol is equivalent to only 35 µg of ethinyl estradiol and should not be used when high-dose (ethinyl estradiol ) estrogen pills are needed; mestranol was the estrogen used in the first oral contraceptive, Enovid). They are usually taken for 21 days with then a seven-day gap during which a withdrawal bleed (often, but incorrectly, referred to as a menstrual period) occurs. These differ in the amount of estrogen given, and whether they are monophasic (the same dose of estrogen and progestogen during each of the 21 days) or multiphasic (varying doses). The introduction of extended-cycle monophasic pills (i.e. Seasonale) has shown that the withdrawal bleeding intervals can be decreased. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「oral contraceptive formulations」の詳細全文を読む スポンサード リンク
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