Because of their ease of use and effectiveness, many women rely on oral contraceptives, or birth control pills, to prevent pregnancy. The Centers for Disease Control estimates that in 2002, 11.6 million women in the United States used oral contraceptives. Most birth control pills contain synthetic forms of the hormones estrogen and progesterone, but a few oral contraceptives contain only progesterone.
Estrogen
In the body, estrogen is responsible for building up the lining of the uterus each month. If pregnancy does not occur, this uterine lining is shed during your monthly period. In a normal cycle, the rise and fall of estrogen stimulates the release of follicle stimulating hormone. FSH is one of the hormones responsible for triggering the release of the egg from the ovary (ovulation). Oral contraceptives keep estrogen at a level that helps suppress the release of FSH.
Most birth control pills contain the estrogen ethinyl estradiol. Norinyl 1/50, Ortho-Novum 1/50 and their generics contain the estrogen mestranol.
Progestin
Progesterone plays the largest role in suppressing ovulation. When progesterone levels drop in the normal menstrual cycle, it triggers the release of FSH and leutinizing hormone, the two hormones responsible for ovulation. The synthetic progesterone, or progestin, in birth control pills keeps progesterone at a high enough level to stop ovulation. Progestin also thickens the mucus in the cervix so that sperm cannot enter the uterus as easily.
Birth control pills vary in the progestin they contain. Most oral contraceptives contain the progestins norethindrone or norgestrel. Ortho-Tri-Cyclen and its generics contain norgestimate. Ethynodiol diacetate is found in Demulen. Desogen, Ortho-Cept and their generics contain desogestrel. Drospirenone is the progestin in Yaz and Yasmin.
Placebo Pills
Birth control pills that combine estrogen and progestin also have a week of placebo, or sugar pills. These pills are usually taken for one week each month, but some pills have a week of placebo pills every three months. This is so you will have a period. The Loestrin brand of pills substitutes the placebo pills with an iron supplement.
Progestin Only Pills
Oral contraceptives that contain only progestin are 95 percent effective in preventing pregnancy, which is slightly lower than the combination pills. Progestin-only pills, also nicknamed "mini-pills," are an option for women who cannot take estrogen, either due to health conditions or because they are breastfeeding. You must take progestin-only pills at the same time each day for maximum effectiveness.
References
- CDC Report: Use of Contraception and Use of Family Planning Services in the United States: 1982--2002
- Basic and Clinical Pharmacology; Bertram Katzung; 2007
- Package Insert for Ortho Micronor
