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.
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:
There are also more dangerous risks from taking birth control pills, although they are rare. These risks include:
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.
Lopez LM, Grimes DA, Gallo MF, Schulz KF. Skin patch and vaginal ring versus combined oral contraceptives for contraception. Cochrane Database Syst Rev. 2008;(1):CD003552.
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.
Amy JJ, Tripathi V. Contraception for women: an evidence based overview. BMJ. 2009;339:b2895.doi:10.1136/bmj.b2895.
Mørch LS, Løkkegaard E, Andreasen AH, Krüger-Kjaer L, Lidegaard O. Hormone therapy and ovarian cancer. JAMA. 2009;302:298-305.