Frequently Asked Questions

What effect do oral contraceptives have on breast cancer risk?

A woman's risk of developing breast cancer depends on several factors, many of which are related to her natural hormones. As oral contraceptives (OCs) alter these hormones, there has been some concern about the effects of OCs on breast cancer risk, especially if taken for many years.

Over the past 15 years, studies have produced inconsistent results, most studies finding no overall increased risk for breast cancer due to OC use. In 1995, researchers at the National Cancer Institute reported an increased risk of developing breast cancer in women under age 35 who had used birth control pills for at least 6 months (compared with those who had never used them). They also saw a slightly lower but still increased risk among women ages 35 to 44. In addition, they found a higher risk among long-term OC users, especially those who had started taking the pill before age 18.

A later comprehensive report analyzed the results of 54 studies conducted in 25 countries that involved 53,297 women with breast cancer and 100,239 women without breast cancer. Researchers found that although there was a slightly increased risk of developing breast cancer in women who were current or recent users of birth control pills, the risk returned to a normal level after 10 years of not using OCs. These study results are considered to be consistent with those of the 1995 study.

The reduction in risk after 10 years or more of being off OCs was consistent regardless of family history of breast cancer, reproductive history, geographic area of residence, ethnic background, differences in study designs, dose and type of hormone, and duration of use. This risk reduction also generally held true for age at first use; however, for reasons that are not yet understood, there was a continued increased risk among women who had started to use OCs before age 20.

NCI, Oral Contraceptives and Cancer Risk, 1997.