Jennifer Kerns, MD, is an assistant professor in the Department of Obstetrics, Gynecology and Reproductive Sciences at the University of California, San Francisco, and a clinical researcher at the university’s Bixby Center for Global Reproductive Health. We spoke with her about some of the many myths we’ve seen online and in the news media about oral contraceptives, also known as birth control pills or simply “the Pill.”
Myth: Oral contraceptives don’t work as well as some other methods to prevent pregnancy.
Dr. Kerns: There are a lot of ways to prevent pregnancy, and the best one is whichever method the woman chooses and uses consistently. It’s true that different methods have different levels of effectiveness, especially when they’re used in real life as opposed to the controlled environment of clinical studies. For example, with perfect use of oral contraceptives, only three in 1,000 women will become pregnant. But typical use is very different. In one year of typical use, 80 in 1,000 women will become pregnant (because of missed doses, for example, or otherwise using the pills inconsistently).
Contraceptive use is what we call a “preference-sensitive decision,” which means that the choice depends on personal factors. The methods are all very different in how they’re used, their effectiveness, and the potential side effects. Different women prioritize different aspects of contraception very differently. Our role as providers is to help a woman identify what her priorities are with respect to the different methods and help her choose the best one for her. If a woman desires oral contraceptives, there is no reason to talk her out of using them.
Myth: Long-term use of oral contraceptives can harm your uterus.
Dr. Kerns: The reality is the complete opposite of this myth. Not only do oral contraceptives not lead to uterine abnormalities, but they actually protect the uterus. We know that oral contraceptives work by suppressing ovulation. In suppressing ovulation, you also suppress the expression of estrogen. Too much estrogen can lead to an abnormal buildup of the lining of the uterus, known as endometrial hyperplasia. We put people on oral contraceptives sometimes when we are worried that they have too much of a buildup of the uterine lining. The woman might be having abnormal bleeding (such as heavier than normal periods) or missed periods. Women who have used oral contraceptives for a long time have a lower risk of both endometrial hyperplasia and uterine cancer (the risk of which is increased by certain types of endometrial hyperplasia). The cancer-preventing benefit of hormonal contraceptives is likely due to the progestin component, which suppresses endometrial proliferation.
Myth: Oral contraceptives cause infertility.
Dr. Kerns: No. A woman returns to whatever her baseline fertility was almost immediately after stopping oral contraceptives. Once a woman stops taking oral contraceptives, which are absorbed in the blood, after a couple of daysher normal hormonal cycle will resume. Keep in mind that some women start taking oral contraceptives long before they want to conceive a child and therefore never know what their baseline fertility is. They may stop the pills when they want to get pregnant and find they have a hard time conceiving, which they then misattribute to the oral contraceptives. The difficulty isn’t from the pills, it’s because of an underlying baseline fertility problem.
Myth: Oral contraceptives carry a high risk of health problems such as blood clots.
Dr. Kerns: The risks associated with oral contraceptives are rare and are far less likely than the health risks associated with pregnancy. For example, women who use oral contraceptives have a two- to four-fold higher risk of deep vein thrombosis, a potentially dangerous type of blood clot in the leg, compared with non-users. But the absolute risk is low overall—about 1 case per 1,000 women per year, which is about half the risk of these clots in pregnant women.
Myth: Oral contraceptives cause cancer.
Dr. Kerns: As stated previously, oral contraceptives lead to a decreased risk of uterine cancer. They also significantly reduce the risk of ovarian cancer. Because they are one of the longest and best-studied medications, we have very good evidence that they are not linked to increased risk of other types of cancer.
[Update: Since the original publication of this interview in November 2017, a large study of Danish women, published Dec. 7, 2017, in the New England Journal of Medicine, linked the use of hormonal contraceptives for five or more years to a slightly increased risk of breast cancer. Dr. Kerns provided the following comment about the new study:
"There are elements of the study design that call into question the validity of the findings. Most notably, the researchers did not control for breastfeeding, which is known to decrease a woman's risk of breast cancer. Women who breastfeed are also less likely to use birth control, as exclusive breastfeeding is a method of birth control. Those women have a lower risk of breast cancer because of the breastfeeding, but in this study, it is impossible to know if their lowered risk was from breastfeeding or from not being on hormonal birth control. Said in another way, it is impossible to know if using hormonal birth control causes an increased risk of breast cancer, or is simply associated with less breastfeeding. Even if we are to assume the findings are valid, the absolute increase in risk of breast cancer among women who used any hormonal birth control method was small—an additional 13 cases per 100,000 women overall, and two per 100,000 women younger than 35 years."]
Myth: If an egg gets fertilized while you are taking oral contraceptives, they will cause a miscarriage by interfering with the egg’s implantation in the uterus.
Dr. Kerns: Oral contraceptives’ major mechanism of action is to suppress ovulation, which means that an egg does not get released from the ovary. In order for an egg to be fertilized, it has to be released in the first place. As to whether that can happen when you are taking oral contraceptives, we know that oral contraceptives are over 99 percent effective when they are used properly. But like every method, they are not 100 percent effective in actual use. There are times when a woman could become pregnant—for example, if she misses pills or takes them inconsistently.
That being said, we don’t think that oral contraceptives have an additional action of preventing implantation in the uterus in the cases when an egg is released and fertilized.The evidence doesn’t suggest there’s an increased risk of miscarriage or problematic implantation in a woman who is taking oral contraceptives, versus a woman who is not. In other words, the idea that the pills somehow cause miscarriage once an egg is fertilized is not supported.
Myth: If you take oral contraceptives while pregnant, it can cause birth defects.
Dr. Kerns: We know very well that this is untrue. Oral contraceptives are one of the best-studied medicationsin the U.S. and internationally. Many women have gotten pregnant while taking oral contraceptives because they took them intermittently or didn’t realize they were already pregnant when they started taking them. Multiple studies have followed women through their pregnancies and childbirth, including one published in 2016 in BMJ. These studies have not found anincreased risk of anomalies in the offspring compared with women who didn’t take oral contraceptives during pregnancy.
Myth: Birth control pills make you gain weight.
Dr. Kerns: Well-designed, double-blind studies comparingoral contraceptives to placebo have found no differences in weight gain. What we do know is that many women who take oral contraceptives are of childbearing age, and many women experience weight gain simply as a result of other natural processes. That might occur at the same time as taking oral contraceptives, but it doesn’t mean there’s a causal effect.
Myth: Oral contraceptives encourage teenagers to have more frequent or more promiscuous sex.
Dr. Kerns: Taking oral contraceptives doesn’t make it more likely that girls will have more sex. This notion is similar to the myth that offering contraception and teaching about it increases the likelihood that people will have sex or have it more often. Many studies have found that this is not true at all.
This opinion does not necessarily reflect the views of the UC Berkeley School of Public Health or of the Editorial Board at BerkeleyWellness.com.
Originally published November 2017. Updated December 2017.