Do Contraceptives Reduce or Increase the Risk of Cancer?

Millions of people regularly take or use contraceptives, such as birth control pills, to avoid unwanted pregnancy or relieve menstruation-related side effects such as cramps or heavy bleeding.  

There is some evidence that contraceptives may affect cancer risk — specifically, that oral contraceptives may increase the likelihood of developing breast and cervical cancers but reduce the risk of endometrial, ovarian, and colorectal cancers. However, much of this evidence comes from observational studies in which populations are observed over time.  

Data from observational studies cannot be relied on as definitive evidence since there may be other variables at play affecting the data. Lifestyle factors such as exercise, smoking, and alcohol use, all have effects on the risk of developing cancer, are difficult to reliably track, and could skew data. 

It’s always best to speak with your physician about medical decisions, including what kind of contraceptive to take if you want or need to. 

Can oral contraceptives affect cancer risk? 

Oral contraceptives, also known as birth control pills, are medications that contain hormones — usually estrogen and progesterone — that, when taken, can prevent pregnancy. These hormones may stop ovulation and prevent sperm from passing the cervix. 

Observational studies have shown that oral contraceptives may increase the likelihood of developing breast and cervical cancers but reduce the risk of endometrial, ovarian, and colorectal cancers. 

While it is not totally understood why this is the case, researchers have proposed a few theories. Since naturally occurring estrogen and progesterone stimulate the growth of some cancers like breast cancer, it’s possible that the synthetic hormones from birth control pills may also increase cancer risk. 

“This subject is tricky because there are a large number of studies on the matter that seem to indicate different risks,” says Colleen Feltmate, MD, a gynecologic oncologist at Dana-Farber Brigham Cancer Center. “Some seem to show that there is not much risk; others suggest long-term use might increase the risk of breast cancer slightly.”   

On the other hand, since oral contraceptives reduce the number of ovulations a person experiences in their lifetime, they may reduce the risk of ovarian cancer by 30 to 50 percent if used for five or more years. Similarly, oral contraceptive pills (OCPs) and progesterone decrease the growth of the endometrial lining and may reduce the risk of developing endometrial cancer by approximately 40 percent with long-term use.  

Can intrauterine devices (IUDs) affect cancer risk? 

An IUD is a small device placed into the uterine cavity to prevent pregnancy. There are two types of IUDs: copper and hormonal. 

Copper IUDs work to prevent pregnancy by preventing sperm from reaching and fertilizing the egg. They are not thought to be associated with an increase or decrease in cancer risk.  

Hormonal IUDs, on the other hand, use hormones such as progesterone to block sperm from passing the cervix and may also stop, or slow down, ovulation. It is thought that they slow cell turnover and growth in the endometrial lining, reducing the risk of endometrial cancers. 

“Many endometrial cancers are often considered to be caused by an excess of estrogen or a lack of progestin,” explains Feltmate. “These cancers, and even their pre-cancers, may to be reversible by the higher progestogenic state that a progesterone IUD creates within the uterus.” 

The hormones released by an IUD keep the uterus lining “quiet” and reduce activity, which decreases the risk of developing cancer. 

Should I take contraceptives if I have or have had cancer? 

Some who are predisposed to developing certain cancers may be recommended to use one type of contraceptive over another. Those with Lynch syndrome, for example, may carry a gene that puts them at higher risk of developing endometrial and ovarian cancers. Specialists in the Lynch Syndrome Center at Dana-Farber provide personalized and comprehensive care and can make recommendations to patients. 

Patients who have breast cancer may be counseled to avoid using hormonal birth control. Feltmate, who works and consult with many patients who are at risk for gynecologic and breast cancers, recommends speaking with a specialist if you carry a genetic marker, like BRCA, that indicates a higher risk of developing certain cancers. 

“There are risks and benefits to any of these contraceptives,” says Feltmate.  

About the Medical Reviewer

Dr. Feltmate is an Assistant Professor of Obstetrics, Gynecology and Reproductive Biology at Harvard Medical School. Her research interests include ovarian cancer, cervical dysplasia and gestational trophoblastic tumors.