Birth control pills come in a variety of formulations. The main division is between combined oral contraceptive pills, containing both estrogens and syntheticprogestogens (progestins), and progestogen only 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 the ovaries from releasing eggs (ovulation). They also thicken the cervical mucus, which keeps sperm from penetrating into the uterus and 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, ethinylestradiol or mestranol,[1][2] in varying amounts, and one of a number of different progestogens. (Regarding the estrogen, the inactive 3-methyl ether of ethinylestradiol, which must be metabolized by the liver into the active ethinylestradiol; 50 μg of mestranol is equivalent to only 35 μg of ethinylestradiol and should not be used when high-dose [50 μg ethinylestradiol] 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.
Monophasic
These are typically given as 21 tablets of estrogen and progestogen, followed by seven tablets of placebo or an iron supplement,[3][4] although some newer formulations contain more active tablets and fewer placebos. Everyday regimens (Microgynon 30 ED, Femodene ED, Logynon ED), which include seven inactive placebo pills, are rarely used in UK practice.[5] Different formulations contain different amounts of estrogen and progestogen:
15 μg ethinylestradiol
60 μg gestodene: 24 days + 4 days placebo (Spain: Melodene-15; Israel: Minesse)[6]
ethinylestradiol/norgestimate combination with 7 tablets 25 μg/180 μg, 7 tablets 25 μg/215 μg, 7 tablets 25 μg/250 μg followed by 7 placebos (Ortho Tri-Cyclen Lo from Ortho-McNeil, Tri-Lo Sprintec back from Teva, Tri-Lo Marzia from Lupin, and norgestimate/ethinylestradiol from Mylan)[9]
ethinylestradiol/desogestrel combination with 7 tablets 25 μg/100 μg, 7 tablets 25 μg/125 μg, 7 tablets 25 μg/150 μg, followed by 7 tablets of ferric oxide (US: Cyclessa, Organon; Velivet, Barr)
20/30/35 μg ethinylestradiol: estrophasic
ethinylestradiol/norethisterone acetate combination with 5 tablets 20 μg/1000 μg, 7 tablets 30 μg/1000 μg, 9 tablets 35 μg/1000 μg, followed by 7 tablets of ferrous fumarate 75 mg (US: Estrostep Fe, Warner Chilcott)
estradiol valerate/dienogest combination with 2 tablets 3 mg/0 mg, followed by 5 tablets 2 mg/2 mg, 17 tablets 2 mg/3 mg, 2 tablets 1 mg/0 mg, and 2 placebos. (AU, EU, RU: Qlaira, US: Natazia, Bayer)[10][11]
Progestogen-only pills
Progestogen-only pills (POPs) use a progestogen alone with doses taken continuously and no or a short gap between packs taken. People who use them may experience irregular light bleeds, and whilst irregular in the first few months of taking, usually settles to a regular pattern in time.
Generally oral contraceptives should not be used in people who currently have the following conditions:
Thrombophlebitis or thromboembolic disorders
A history of deep vein thrombophlebitis or thromboembolic disorders
Cerebrovascular or coronary artery disease (current or history)
Valvular heart disease with thrombogenic complications
Severe hypertension
Diabetes with vascular involvement
Headaches with focal neurological symptoms
Major surgery with prolonged immobilization
Known or suspected carcinoma of the breast or personal history of breast cancer
Carcinoma of the endometrium or other known or suspected estrogen-dependent neoplasia
Undiagnosed abnormal genital bleeding
Cholestatic jaundice of pregnancy or jaundice with prior pill use
Hepatic adenomas or carcinomas, or active liver disease
Known or suspected pregnancy
Hypersensitivity to any component of the product
More comprehensive guidelines that include analysis of risks and benefits can be found in the World Health Organization Medical Eligibility for Contraceptive Use Guidelines[12] which are reflected in the CDC Medical Eligibility for Contraceptive Use Guidelines.[13]
^Hatcher, Robert A.; Nelson, Anita (2004). "Combined Hormonal Contraceptive Methods". In Hatcher; Robert A. (eds.). Contraceptive Technology (18th rev. ed.). New York: Ardent Media. pp. 391–460. ISBN0-9664902-5-8.
^Speroff, Leon; Darney, Philip D. (2005). "Oral Contraception". A Clinical Guide for Contraception (4th ed.). Philadelphia: Lippincott Williams & Wilkins. pp. 21–138. ISBN0-7817-6488-2.
^Serge Herceberg; Paul Preziosi; Pilar Galan. "Iron deficiency in Europe"(PDF). Public Health Nutrition: 4(2B). pp. 537–545. Archived from the original(PDF) on 2011-07-26. Retrieved 2010-11-19.
