Birth control pills (BCPs) contain man-made forms of two hormones called estrogen and progestin. These hormones are made naturally in a woman's ovaries. Birth control pills can contain both of these hormones, or have progestin only.
Both hormones prevent a woman's ovary from releasing an egg during her menstrual cycle (called ovulation). They do this by changing the levels of the natural hormones the body makes.
Progestins also make the mucus around a woman's cervix thick and sticky. This helps prevent sperm from entering the uterus.
Contraception - pills - hormonal methods; Hormonal birth control methods; Birth control pills; Contraceptive pills; BCP; OCP
Birth control pills are also called oral contraceptives or just "the pill." A health care provider must prescribe birth control pills.
The "mini-pill" is a type of birth control pill that contains only progestin, no estrogen. These pills are an option for women who do not like the side effects of estrogen or who cannot take estrogen for medical reasons.
They can also be used after delivery in women who are breast-feeding.
All women who take birth control pills need a check-up at least once a year. Women should also have their blood pressure checked 3 months after they begin to take the pill.
Birth control pills only work well if the woman remembers to take her pill daily without missing a day. Only 2 or 3 women out of 100 who take birth control pills correctly for a year will get pregnant.
Birth control pills may cause many side effects. These include:
Changes in menstrual cycles, no menstrual cycles, extra bleeding
Nausea, mood changes, worsening of migraines (mostly due to estrogens)
Breast tenderness and weight gain
Rare but dangerous risks from taking birth control pills include:
High blood pressure
Birth control pills without estrogen are much less likely to cause these problems. The risk is higher for women who smoke or have a history of high blood pressure, clotting disorders, or unhealthy cholesterol levels. However, the risk of these complications are much lower with either type of pill than with pregnancy.
Regular menstrual cycles will return within 3 to 6 months after a woman stops using most hormonal birth control methods.
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Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Bellevue, WA; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.