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Oral Contraceptives and Cancer Risk: Questions and Answers 

Introduction 

Oral contraceptives (OCs) first became available to American women in the early 1960s. 

The convenience, effectiveness, and reversibility of action of birth control pills 

(popularly known as “the pill”) have made them the most popular form of birth control in 

the United States. However, concerns have been raised about the role that the hormones 

in OCs might play in a number of cancers, and how hormone-based OCs contribute to 

their development. Sufficient time has elapsed since the introduction of OCs to allow 

investigators to study large numbers of women who took birth control pills for many 

years. 

This fact sheet addresses only what is known about OC use and the risk of developing 

cancer. It does not deal with other serious side effects of OC use, such as the increased 

risk of cardiovascular disease for certain groups of women. Recently, alternative 

methods of delivering hormones for contraception have been developed, including a 

topical patch, vaginal ring, and intrauterine delivery system, but these products are too 

new to have been tested in clinical trials (research studies) for long-term safety and other 

effects (1). They also are not covered in this fact sheet. 

Key Points 

• Some cancers depend on naturally occurring sex hormones for their development 

and growth. Researchers are interested in learning whether the hormones in oral 

contraceptives affect cancer risk in women (see Question 1). 

• Some studies have shown an increased risk of breast cancer in women taking oral 

contraceptives, while other studies have shown no change in risk (see Question 2). 

• Oral contraceptive use has been shown in multiple studies to decrease the risk of 

ovarian and endometrial cancer (see Question 3). 

• Oral contraceptives have been shown to increase the risk of cervical cancer; 

however, human papillomavirus is the major risk factor for this disease (see 

Question 4). 

• The risk of liver cancer is increased in women who take oral contraceptives and 

are otherwise considered low risk for the disease (see Question 5). 
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1. What types of oral contraceptives are available in the United States? Why do 

researchers believe that oral contraceptives may influence cancer risk? 

Currently, two types of OCs are available in the United States. The most commonly 

prescribed OC contains two man-made versions of natural female hormones (estrogen 

and progesterone) that are similar to the hormones the ovaries normally produce. This 

type of pill is often called a “combined oral contraceptive.” The second type of OC 

available in the United States is called the minipill. It contains only a type of 

progesterone. 

Estrogen stimulates the growth and development of the uterus at puberty, causes the 

endometrium (the inner lining of the uterus) to thicken during the first half of the 

menstrual cycle, and influences breast tissue throughout life, but particularly from 

puberty to menopause. 

Progesterone, which is produced during the last half of the menstrual cycle, prepares the 

endometrium to receive the egg. If the egg is fertilized, progesterone secretion continues, 

preventing release of additional eggs from the ovaries. For this reason, progesterone is 

called the “pregnancy-supporting” hormone, and scientists believe that it has valuable 

contraceptive effects. The man-made progesterone used in OCs is called progestogen or 

progestin. 

Because medical research suggests that some cancers depend on naturally occurring sex 

hormones for their development and growth, scientists have been investigating a possible 

link between OC use and cancer risk. Researchers have focused a great deal of attention 

on OC users over the past 40 years. This scrutiny has produced a wealth of data on OC 

use and the development of certain cancers, although results of these studies have not 

always been consistent. The risk of endometrial and ovarian cancers is reduced with the 

use of OCs, while the risk of breast and cervical cancers is increased (1). A summary of 

research results for each type of cancer is given in Questions 2–5. 

2. How do oral contraceptives affect breast cancer risk? 

A woman’s risk of developing breast cancer depends on several factors, some of which 

are related to her natural hormones. Hormonal factors that increase the risk of breast 

cancer include conditions that may allow high levels of hormones to persist for long 

periods of time, such as beginning menstruation at an early age (before age 12), 

experiencing menopause at a late age (after age 55), having a first child after age 30, and 

not having children at all. 

A 1996 analysis of worldwide epidemiologic data conducted by the Collaborative Group 

on Hormonal Factors in Breast Cancer found that women who were current or recent 

users of birth control pills had a slightly elevated risk of developing breast cancer. The 

risk was highest for women who started using OCs as teenagers. However, 10 or more 

years after women stopped using OCs, their risk of developing breast cancer returned to 

the same level as if they had never used birth control pills, regardless of family history of 

breast cancer, reproductive history, geographic area of residence, ethnic background, 
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differences in study design, dose and type of hormone, or duration of use. In addition, 

breast cancers diagnosed in women after 10 or more years of not using OCs were less 

advanced than breast cancers diagnosed in women who had never used OCs. To conduct 

this analysis, the researchers examined the results of 54 studies. The analysis involved 

53,297 women with breast cancer and 100,239 women without breast cancer. More than 

200 researchers participated in this combined analysis of their original studies, which 

represented about 90 percent of the epidemiological studies throughout the world that had 

investigated the possible relationship between OCs and breast cancer (2). 

The findings of the Women’s Contraceptive and Reproductive Experiences (Women’s 

CARE) study were in contrast to those described above. The Women’s CARE study 

examined the use of OCs as a risk factor for breast cancer in women ages 35 to 64. 

Researchers interviewed 4,575 women who were diagnosed with breast cancer between 

1994 and 1998, and 4,682 women who did not have breast cancer. Investigators 

collected detailed information about the participants’ use of OCs, reproductive history, 

health, and family history. The results, which were published in 2002, indicated that 

current or former use of OCs did not significantly increase the risk of breast cancer. The 

findings were similar for white and black women. Factors such as longer periods of use, 

higher doses of estrogen, initiation of OC use before age 20, and OC use by women with 

a family history of breast cancer were not associated with an increased risk of the disease 

(3). 

In a National Cancer Institute (NCI)-sponsored study published in 2003, researchers 

examined risk factors for breast cancer among women ages 20 to 34 compared with 

women ages 35 to 54. Women diagnosed with breast cancer were asked whether they 

had used OCs for more than 6 months before diagnosis and, if so, whether the most 

recent use had been within 5 years, 5 to 10 years, or more than 10 years. The results 

indicated that the risk was highest for women who used OCs within 5 years prior to 

diagnosis, particularly in the younger group (4). 

3. How do oral contraceptives affect ovarian and endometrial cancer risk? 

Studies have consistently shown that using OCs reduces the risk of ovarian cancer. In a 

1992 analysis of 20 studies of OC use and ovarian cancer, researchers from Harvard 

Medical School found that the risk of ovarian cancer decreased with increasing duration 

of OC use. Results showed a 10 to 12 percent decrease in risk after 1 year of use, and 

approximately a 50 percent decrease after 5 years of use (5). 

Researchers have studied how the amount or type of hormones in OCs affects ovarian 

cancer risk reduction. One of the studies used in the Harvard analysis, the Cancer and 

Steroid Hormone Study (CASH), found that the reduction in ovarian cancer risk was the 

same regardless of the type or amount of estrogen or progestin in the pill (6). A more 

recent analysis of data from the CASH study, however, indicated that OC formulations 

with high levels of progestin reduced ovarian cancer risk more than preparations with low 

progestin levels (7). In another recent study, the Steroid Hormones and Reproductions 

(SHARE) study, researchers investigated new, lower-dose progestins that have varying 
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androgenic properties (testosterone-like effects). They found no difference in ovarian 

cancer risk between androgenic and nonandrogenic pills (8). 

OC use in women at increased risk of ovarian cancer due to BRCA1 and BRCA2 genetic 

mutations has been studied. One study showed a reduction in risk, but a more recent 

study showed no effect (9, 10). 

The use of OCs has been shown to significantly reduce the risk of endometrial cancer. 

This protective effect increases with the length of time OCs are used, and continues for 

many years after a woman stops using OCs (11). 

4. How do oral contraceptives affect cervical cancer risk? 

Evidence shows that long-term use of OCs (5 or more years) may be associated with an 

increased risk of cancer of the cervix (the narrow, lower portion of the uterus) (12). 

Although OC use may increase the risk of cervical cancer, human papillomavirus (HPV) 

is recognized as the major cause of this disease. Approximately 14 types of HPV have 

been identified as having the potential to cause cancer, and HPVs have been found in 

99 percent of cervical cancer biopsy specimens worldwide (12). More information about 

HPV and cancer is available in Human Papillomaviruses and Cancer: Questions and 

Answers at http://www.cancer.gov/cancertopics/factsheet/risk/HPV on the Internet. 

A 2003 analysis by the International Agency for Research on Cancer (IARC) found an 

increased risk of cervical cancer with longer use of OCs. Researchers analyzed data from 

28 studies that included 12,531 women with cervical cancer. The data suggested that the 

risk of cervical cancer may decrease after OC use stops (13). In another IARC report, 

data from eight studies were combined to assess the effect of OC use on cervical cancer 

risk in HPV-positive women. Researchers found a fourfold increase in risk among 

women who had used OCs for longer than 5 years. Risk was also increased among 

women who began using OCs before age 20 and women who had used OCs within the 

past 5 years (14). The IARC is planning a study to reanalyze all data related to OC use 

and cervical cancer risk (12). 

 

5. How do oral contraceptives affect liver cancer risk? 

Several studies have found that OCs increase the risk of liver cancer in populations 

usually considered low risk, such as white women in the United States and Europe who 

do not have liver disease. In these studies, women who used OCs for longer periods of 

time were found to be at increased risk for liver cancer. However, OCs did not increase 

the risk of liver cancer in Asian and African women, who are considered high risk for this 

disease. Researchers believe this is because other risk factors, such as hepatitis infection, 

outweigh the effect of OCs (15). 
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6. What screening tests are available for the cancers described? 

Studies have found that regular breast cancer screening with mammograms reduces the 

number of deaths from breast cancer for women ages 40 to 69. Women who are at 

increased risk for breast cancer should seek medical advice about when to begin having 

mammograms and how often to be screened. A high-quality mammogram, with a 

clinical breast exam (an exam done by a professional health care provider), is the most 

effective way to detect breast cancer early. 

Abnormal changes in the cervix can often be detected by a Pap test and treated before 

cancer develops. Women who have begun to have sexual intercourse or are age 21 

should check with their doctor about having a Pap test. Researchers are working on 

developing screening tests for ovarian and endometrial cancer. 

Women who are concerned about their risk for cancer are encouraged to talk with their 

health care provider. More information is also available from the Cancer Information 

Service (see below). 

Selected References

1. Burkman R, Schlesselman JJ, Zieman M. Safety concerns and health benefits associated 

with oral contraception. American Journal of Obstetrics and Gynecology 2004; 

190(4 Suppl):S5–22. 

2. Collaborative Group on Hormonal Factors in Breast Cancer. Breast cancer and hormonal 

contraceptives: Collaborative reanalysis of individual data on 53,297 women with breast 

cancer and 100,239 women without breast cancer from 54 epidemiological studies. 

Lancet 1996; 347:1713–1727. 

3. Marchbanks PA, McDonald JA, Wilson HG, et al. Oral contraceptives and the risk of 

breast cancer. New England Journal of Medicine 2002; 346(26):2025–2032. 

4. Althuis MD, Brogan DD, Coates RJ, et al. Breast cancers among very young 

premenopausal women (United States). Cancer Causes and Control 2003; 14(2): 

151–160. 

5. Hankinson SE, Colditz GA, Hunter DJ, et al. A quantitative assessment of oral 

contraceptive use and risk of ovarian cancer. Obstetrics and Gynecology 1992; 

80(4):708–714. 

6. Centers for Disease Control and Prevention and the National Institute of Child Health and 

Human Development. The reduction in risk of ovarian cancer associated with oralcontraceptive use. The Cancer and Steroid Hormone Study of the Centers for Disease 

Control and the National Institute of Child Health and Human Development. New 

England Journal of Medicine 1987; 316(11):650–655. 
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7. Schildkraut JM, Calingaert B, Marchbanks PA, Moorman PG, Rodriguez GC. Impact of 

progestin and estrogen potency in oral contraceptives on ovarian cancer risk. Journal of 

the National Cancer Institute 2002; 94(1):32–38. 

8. Greer JB, Modugno F, Allen GO, Ness RB. Androgenic progestins in oral contraceptives 

and the risk of epithelial ovarian cancer. Obstetrics and Gynecology 2005; 105(4): 

731–740. 

9. Narod SA, Risch H, Moslehi R, et al. Oral contraceptives and the risk of hereditary 

ovarian cancer. Hereditary Ovarian Cancer Clinical Study Group. New England Journal 

of Medicine 1998; 339(7):424–428. 

10. Modan B, Hartge P, Hirsh-Yechezkel G, et al. Parity, oral contraceptives, and the risk of 

ovarian cancer among carriers and noncarriers of a BRCA1 or BRCA2 mutation. New 

England Journal of Medicine 2001; 345(4):235–240. 

11. Emons G, Fleckenstein G, Hinney B, Huschmand A, Heyl W. Hormonal interactions in 

endometrial cancer. Endocrine-Related Cancer 2000; 7(4):227–242. 

12. Franceschi S. The IARC commitment to cancer prevention: The example of 

papillomavirus and cervical cancer. Recent Results in Cancer Research 2005; 166: 

277–297. 

13. Smith JS, Green J, Berrington de GA, et al. Cervical cancer and use of hormonal 

contraceptives: A systematic review. Lancet 2003; 361(9364):1159–1167. 

14. Moreno V, Bosch FX, Munoz N, et al. Effect of oral contraceptives on risk of cervical 

cancer in women with human papillomavirus infection: The IARC multicentric 

case-control study. Lancet 2002; 359(9312):1085–1092. 

15. Yu MC, Yuan JM. Environmental factors and risk for hepatocellular carcinoma. 

Gastroenterology 2004; 127(5 Suppl 1):S72–S78. 

# # # 

Related Resources

Publications (available at http://www.cancer.gov/publications) 

• National Cancer Institute Fact Sheet 3.20, Human Papillomaviruses and Cancer: 

Questions and Answers

• What You Need To Know AboutTM Breast Cancer 

• What You Need To Know AboutTM Cancer of the Cervix
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National Cancer Institute (NCI) Resources

Cancer Information Service (toll-free)

 Telephone: 1–800–4–CANCER (1–800–422–6237) 

 TTY: 1–800–332–8615 

Online 

NCI’s Web site: http://www.cancer.gov 

LiveHelp, NCI’s live online assistance: 

https://cissecure.nci.nih.gov/livehelp/welcome.asp

This fact sheet was reviewed on 5/4/06