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Reviewed by the Faculty of Harvard Medical School

Risks Of Combination Birth-Control Pills

Temporary Side Effects

Side effects of combination birth-control pills may include:
  • Nausea
  • Spotting or irregular bleeding
  • Breast tenderness
  • Mood changes
  • Headaches

Over time, these side effects usually become less troublesome, improving or disappearing within about three months. Contact your health-care provider if the symptoms do not improve.

Women considering the birth-control pill often worry about the potential for developing breast cancer. This possible relationship is still being studied.

Published reports have stated opposite conclusions, which lead to more fear and confusion. Some studies show that current and recent use of the combination pill may be associated with a 20-percent increased risk of "early breast cancer," that is, breast cancer diagnosed before the onset of menopause. "Recent use" means the pill was used within the past one to five years.

Although a 20-percent increase seems large, the actual number of breast cancer cases was small. Fortunately, the number of cases of breast cancer diagnosed in women younger than 40 has been steadily dropping since 1985. Most studies show that the overall risk of breast cancer does not increase with the number of years a woman uses the pill.

Furthermore, the pill does not increase the risk of developing cancer in women with a family history of breast cancer or a personal history of benign breast disease.

Who Should Not Use Combination Birth-Control Pills

Women who should not use the birth-control pill are said to have "absolute contraindications," meaning that there are known medical reasons NOT to use the combination pill. Two very serious absolute contraindications include:
  • Arterial Clotting. Arterial clotting events, also known as arterial thrombosis, include stroke, heart attack and medical conditions that increase the chance of stroke or heart attack. Arteries are bigger than veins and have muscles within their walls that actively move blood forward in one direction, away from the heart. Because estrogen increases the production and number of clotting factors in the blood, a clot may form more easily inside an artery, dangerously blocking blood flow. Blood clots can stop the flow of blood and cause heart attack or stroke. Progestins, unlike estrogens, do not increase the production of clotting factors.
    Low doses of estrogen are less likely to cause arterial thrombosis than are higher doses. Newer birth-control pills contain lower amounts of estrogen and are less dangerous. These low-dose combination pills have less than 50 micrograms of estrogen and are safe for healthy, young women who do not smoke. However, arterial clots are more likely to form in women taking the combination pill whose health is poor, particularly women older than 35.
    Although smoking is unhealthy at any age, it greatly increases the risk of clots in women of any age who use the birth-control pill. Women who are older than 35, in poor health and using combination birth-control pills are have the highest risk of arterial clotting.
  • Venous Inflammation And Clotting. Veins are thin-walled blood vessels that carry blood back toward the heart. The movement of blood in the veins is passive, and the flow can become sluggish, leading to the formation of blood clots. Blood clots may also form if the body's natural clotting system is defective.
    The risk of venous thrombosis (clotting in the veins) is related to the amount of estrogen in the birth-control pill, and not to progestin hormone, or smoking tobacco. Women who use a low-dose combination pill have a slightly higher risk of developing arterial or venous clots.
    Some women have an inherited tendency to form clots in the veins. Normally, the body produces "factor V Leiden," a substance made by the liver that helps the body to form clots and prevents excessive bleeding when there is an injury. A genetic defect may alter the normal form of factor V Leiden so that blood clots are more likely to form even when there is no injury.
    Women with this defect are 6 to 8 times more likely to develop venous clots than are women without the defect. Women with this defect who use the combination pill are 30 times more likely to form venous clots.
    Because venous thrombosis is not very common, genetic testing for this defect is not routinely offered, and a woman may not know that she has it. However, women who have a history of venous thrombosis or who have a close relative with this condition are advised not to use the combination birth control.

Women with any of these risk factors should have genetic testing for specific inherited clotting defects.

Other Cautions

Women should not use combination birth-control pills if they:
  • Have poor liver function or active inflammation of the liver
  • Have undiagnosed abnormal vaginal bleeding
  • Are or suspect they may be pregnant
  • Smoke and are older than 35
  • Have elevated blood pressure

More reasons to think carefully about using combination birth-control pills:

  • Migraine headaches
  • High blood pressure, particularly if it is not well controlled
  • Uterine fibroids
  • Diabetes or history of gestational diabetes during a past pregnancy
  • Epilepsy
  • Gallbladder disease
  • Obstructive jaundice (mechanical blockage of the liver's drainage system that results in yellowing of the skin from the back up of liver juices or bile)
  • Sickle cell disease or sickle C disease
  • Scheduled major surgery that requires a long period of immobility during recovery
Last updated October 1, 2010




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