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Oral Contraceptives and Cancer Risk

Peer Review Status: Holden Comprehensive Cancer Center, Cancer Information Service
First Published: April 2002
Last Revised: April 2003

The question of whether oral contraceptives or birth control pills cause cancer is an important one for men and women choosing their method of family planning. In looking for an answer to the question, one can find that oral contraceptives and cancer risk has been studied extensively.

The studies showed that the longer a woman takes birth control pills, the lower her chance of developing ovarian cancer. Many studies demonstrated a 40-50% reduction of risk for ovarian cancer.

These studies also found that use of oral contraceptives may protect against endometrial (uterine lining) cancer. Some researchers found that this protective effect increased with the length of time the pills were taken.

The reduction in risk of ovarian cancer and endometrial cancers from oral contraceptives does not apply to the sequential type of pill. Sequential oral contraceptives were taken off the market in 1976. Women on sequential birth control pills took 16 days of estrogen, followed by 5 days of estrogen plus progesterone pills.

There is some evidence that long-term use of oral contraceptives may increase the risk of cervical cancer. The results of studies by National Cancer Institute (NCI) scientists support a relationship between extended use of the pill (5 or more years) and a slightly increased risk of cervical cancer. However, the exact nature of this association between oral contraceptive use and risk of cervical cancer is unclear.

The risk of breast cancer and oral contraceptive use has been studied closely because hormonal factors are known to influence the development of breast cancer risk. Birth control pill use was found to slightly increase the risk of breast cancer. An NCI study reported an increased risk of developing breast cancer among women under age 35 who had used oral contraceptives for at least six months, compared to those who had had never used oral contraceptives. This study showed a higher risk among long-term oral contraceptive users, especially those who began taking the pill before age 18.

The long-term effect of the current pill formulations will not be fully sorted out for years to come. Any decision to use oral contraceptives should be made in light of a woman's total health, including her other risk factors and the impact of an unwanted pregnancy