Birth control pills (BCPs) contain man-made forms of hormones that are normally made in a woman's ovaries. These hormones are called estrogen and progestin. Birth control pills will have either both of these hormones, or 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 help prevent sperm from entering the uterus by making the mucus around a woman's cervix thick and sticky.
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 most common type of birth control pill combines the hormones estrogen and progestin. There are many different forms of this type of birth control pill.
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.
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 pills 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
There are also more dangerous risks from taking birth control pills, although they are rare. These risks include:
High blood pressure
Birth control pills with estrogen are much more 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.
Once a woman stops using most hormonal birth control methods, she will go back to her former menstrual cycles within 3 to 6 months.
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Spencer AL, Bonnema R, McNamara MC. Helping women choose appropriate hormonal contraception: update on risks, benefits, and indications. Am J Med. 2009;122:497-506.
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Mørch LS, Løkkegaard E, Andreasen AH, Krüger-Kjaer L, Lidegaard O. Hormone therapy and ovarian cancer. JAMA. 2009;302:298-305.
Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Bellevue, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.