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Oral Contraceptives


Janet Gray, Ph.D.
Janet Gray, Ph.D.

As author of our 2008 and 2010 State of the Evidence reports, Dr. Gray drives the science behind all our work.

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Health Care Exposures

Advances in health care have been extraordinarily helpful in prolonging our lives and providing better quality of life. But some medical advances have a downside: they can sometimes inadvertently expose us to risk factors that could lead to cancer or other illnesses.

Following are some of the health-care related risk factors. Check out our Tips for Prevention section to learn how you might reduce your risk.

Ionizing Radiation


Learn how to make educated health care choices and reduce your breast cancer risk.

Tips for making informed healthcare choices >

Ionizing radiation (X-rays and gamma radiation) has long been known to cause breast cancer, both by directly damaging DNA and by disrupting normal cellular and intra-cellular processes. There is no safe dose of radiation and the genetic damage caused by radiation accumulates over a lifetime.

Medical radiation exposures in children raise particular concerns: equipment is usually designed for (larger) adults, children are more sensitive to radiation, and kids have more years ahead of them for radiation to add up and impact health.

Women who have BRCA1 and BRCA2 mutations (the "breast cancer genes") may also be more sensitive to radiation exposure. Yet these women are often screened for breast cancer more often and at earlier ages, raising genuine concerns about the use of radiation-based screening methods for breast cancer among this group.

Hormone Replacement Therapy (HRT)

The International Agency for Research on Cancer (IARC) has listed estrogens as known human carcinogens since 1987, and the National Toxicology Program (NTP) added HRT and estrogens used in oral contraceptives to the list of known human carcinogens in 2002.

Oral Contraceptives

Oral contraceptives have been shown to increase breast cancer risk, especially among current and recent users who have used them for more than five years, premenopausal women, and those with a family history of breast cancer. However, postmenopausal women who have discontinued use for at least a decade show no significant increase in rates.

Infertility drugs

Infertility drugs as a group have not been clearly linked to breast cancer, although a few studies have linked high doses of the drug clomiphene citrate to later-life risk of breast cancer. Young women who begin infertility treatments early may also be at increased risk of later-life breast cancer, although studies cannot rule out a separate factor that leads to both infertility and long-term breast cancer risk in these women.


Diethylstilbestrol (DES) offers the clearest evidence that a synthetic estrogen can increase risk of cancer. It was prescribed until 1971 to prevent miscarriages but was banned when daughters of women who took the drug were found to have higher rates of an extremely rare cancer.


Phthalates are a group of endocrine-disrupting chemicals found in PVC or #3 plastic, including plastic medical tubing. Phthalate exposure has been linked to early puberty in girls, a risk factor for later-life breast cancer. Some phthalates also act as weak androgens and estrogens in laboratory studies.

Ethylene Oxide

Ethylene oxide is used in the sterilization of medical equipment and is commonly used to manufacture popular brands of shampoo. It is classified as a known human carcinogen and is one of the 51 chemicals that the National Toxicology Program (NTP) identifies as mammary carcinogens in animals.


Bisphenol A (BPA) is one of the most pervasive chemicals in modern life. It’s a building block of polycarbonate plastic and epoxy resins, and is used in medical devices and as a dental sealant. Research shows that BPA exposure is linked to breast cancer.


Mercury is found in some dental fillings. Higher accumulations of mercury and other metals have been found in cancerous breast biopsies as compared to biopsies taken from women without breast cancer. Lab studies have shown that methyl mercury can disrupt hormone-regulated cellular processes.