If you're trying to prevent pregnancy, considering the form of birth control you'll use involves a variety of factors — from the impact on menstrual cycles to any potential side effects. Over the last few decades, as we've learned more about hormonal birth control and studied its impact on health (in many cases, lack thereof), companies have developed newer formulations of birth control with lower hormone doses. In that same time, closer investigation of all the data has revealed the overall safety of hormonal birth control for most people.
Since 14% of people assigned "female" at birth in the US ages 15-44 currently use combined oral contraceptives (aka the pill), we're summarizing the evidence from epidemiological studies on birth control and different types of cancers. We're also covering the current theories for why the synthetic hormones in birth control might affect your cancer risks — and we’re putting these risks into perspective as you consider your own birth control decisions.
Here are the key takeaways:
- Hormonal birth control can affect our hormone receptors and lead to either an increased or decreased risk of certain cancers. We have the most data regarding combined oral contraceptives (aka the pill) in particular, though early research shows other forms of hormonal birth control likely have the same associations with cancer.
- The birth control pill has been shown to slightly increase the risk of breast cancer. One study estimated that it increased the incidence of breast cancer by 13 cases per 100,000 contraceptive users per year.
- The pill has also been associated with a slightly increased risk of cervical cancer. That said, research finds that this increased risk fades with time — and 10 or more years after discontinuing use of the pill, previous oral contraceptive users have the same risk as those who never used the pill. (We don't have any real-world data demonstrating how this increased risk actually plays out.)
- The pill, on the flip side, reduces the risk of endometrial and ovarian cancer (the former of which is especially helpful for people with polycystic ovary syndrome). Recent research estimated that it prevented the incidence of endometrial cancer by 276 cases and ovarian cancer by 52 cases in a population of two million.
- For many people, the benefits of reliable pregnancy prevention that come from hormonal birth control outweigh the potential increased risks.
"If the goal is to avoid an unintended pregnancy, then for the general population without a family history of breast cancer, the benefits of hormonal contraception outweigh the risks," explains OB-GYN and Modern Fertility medical advisor Dr. Eva Luo, MD, MBA. "For those with a baseline increased risk of breast cancer, an individualized discussion with your doctor is important to find the best form of contraception for you."
A note before we dive in
Combined oral contraceptives (COCs), which contain both estrogen- and progesterone-like synthetic hormones, have dominated the birth control market for decades. Because of this, most of the data collected on birth control and cancer has been on “the pill.” In this article, we're focusing on COCs and cancer. While early research shows that other forms of hormonal birth control likely have the same relationship with cancer, non-hormonal forms of birth control (like the copper intrauterine device or barrier methods like condoms) don't have the same associated risks.
First up: Why is there a relationship between the pill and cancer?
In 1999, the International Agency for Research on Cancer classified the birth control pill as carcinogenic to humans — but, over time, research has shown us that the umbrella term "carcinogenic" is misleading.
Unlike a run-of-the-mill carcinogen that causes cancer by damaging our cells or DNA, it’s hypothesized that the pill — which contains synthetic steroids that resemble the hormones our bodies produce — influences our cancer risks mainly by activating the receptors in cells that hormones bind to. This has a unique downstream effect on different types of reproductive tissue:
- Breast cancer: There's strong data that suggests that estrogens can stimulate the growth of breast cancer cells. Progestins might also have a role here, but more research is needed to determine their contribution. (Both of these synthetic hormones are in the pill.)
- Cervical cancer: We don't know exactly why there may be a relationship between the hormones in contraceptives and cervical cancer. There's one theory, though, that's only been tested in rodents: Contraceptive hormones might make cervical tissue more susceptible to human papillomavirus (HPV), which would increase the probability of developing cervical cancer.
- Ovarian cancer: There are multiple theories for how birth control could lower the risk of ovarian cancer, one of which is the hypothesis that ovulation causes "microtrauma" to the ovaries, which could then lead to cancer. By preventing the body from ovulating through birth control, it reduces that microtrauma.
- Endometrial cancer (aka uterine cancer): Although estrogen encourages the growth of endometrial cells, research suggests that progestins can block this effect and reduce the risk of cancer.
Here's a simpler way to explain this: The synthetic hormones in birth control bind to the cells of different types of reproductive tissue. Those synthetic hormones will either encourage or block the growth of cells in tissue — creating an easier or more challenging path for cancer to develop.
Can birth control increase the risk of certain cancers?
Before we talk about some of the increased risks associated with hormonal birth control, it's important to note that decisions around medications often require the weighing of all of the upsides against the downsides. For many people, the security of an effective form of birth control outweighs the potential risks — and, as we'll cover in the next section, there are also decreased risks that come with hormonal birth control.
"The actual absolute number of patients affected by this slight increase is overall small," says Dr. Luo. "As a result, [it's] still worth taking a form of hormonal birth control to effectively prevent an unwanted pregnancy."
Your healthcare provider can help you consider all of this information — along with personal health factors like bleeding patterns, health conditions, and how you prefer to take contraceptives — as you decide on the right birth control option for you.
Hormonal birth control may slightly increase the risk of breast cancer
Other than skin cancer, breast cancer is the most common cancer among those assigned "female" at birth:
- Although the topic is still hotly debated, research has linked oral contraception with an increased breast cancer risk.
- In one example cohort study of 1.8 million Danish women, those who either currently or previously used hormonal contraception had a 20% higher risk of breast cancer.
- The research is mixed on whether or not how long someone was on hormonal contraception impacts this increased risk. The Danish study we mentioned above found that the risk increased with years spent on contraception, but a 2010 review that evaluated studies made up of hundreds of thousands of people found that the risk of breast cancer actually went back to baseline between five and ten years after stopping.
- A recent meta-analysis found that BRCA1 or BRCA2 genes (mutations that put people at increased risk for breast and ovarian cancer) do not significantly amplify the risk of hormonal birth control on breast cancer. In other words, for those of us with BRCA1 or BRCA2, combined oral contraceptives might offer extra protection against ovarian cancer without significantly increasing the risk of breast cancer.
If you’re looking for perspective on how this risk plays out in real life, in a population of close to two million people assigned "female" at birth, it was estimated that oral contraceptives may have increased the incidence of breast cancer by 135 cases (that's 135 compared to two million possible cases).
All of this said, adds Dr. Luo, "Breast cancer has a well-established and effective screening program: clinical breast exams with a clinician every 1-2 years and after the age of 40, annual mammograms." This proactive screening provides opportunities for breast cancer to be detected at an earlier stage (though it's important to remember that the actual overall risk while on hormonal birth control is small).
There's also likely a slightly increased risk of cervical cancer
Of all the cancers that might be impacted by birth control, cervical cancer is the least common in the general population. A pooled analysis of 24 studies that examined the relationship between hormonal contraceptives and cervical cancer found a small but significant increased risk. This risk decreases after discontinuation of birth control, matching that of someone who’s never taken the pill after 10 years.
It's unlikely that liver cancer risk increases with birth control
The association between liver cancer risk and hormonal contraception may be an artifact of outdated, high-dose birth control formulations. Although early studies found a significantly increased risk of liver cancer in birth control users, a recent meta-analysis (which pools together data from multiple different studies) of 17 articles on this topic failed to find any significant relationships. We still need more research here.
Can birth control reduce the risk of certain cancers?
Here's where the cost-benefit analysis comes back into play — while hormonal birth control may be linked to an increased risk for certain cancers, it's also linked to a reduced risk in other types.
Hormonal birth control likely reduces the risk of endometrial cancer
A large number of studies have looked into birth control’s ability to lower the risk for endometrial (aka uterine) cancer:
- Meta-analyses indicate that birth control could lower your risk for endometrial cancer by about 25%. (Most of the reviewed studies only included people taking combined estrogen and progestin pills.)
- One study that included over 250,000 women found that the longer a person uses oral contraceptives, the greater the reduction in endometrial cancer risk. Additionally, this risk reduction lasts for more than 30 years after discontinuing birth control — with the average age of an endometrial cancer diagnosis at 63 years.
- A 2016 review found that this association was especially true for people with polycystic ovary syndrome (PCOS). People with PCOS are more likely to be diagnosed with endometrial cancer. Why? Irregular ovulation, which is a hallmark of the condition, can lead to estrogen acting on the endometrium without the presence of progesterone to keep it in check. Hormonal birth control can resolve that issue by introducing synthetic progestins into the body, thereby decreasing the risk of endometrial cancer.
Let's consider this reduced risk in real-world outcomes like we did the risk of breast cancer: That same 2018 study estimated oral contraceptives prevented 276 cases of endometrial cancer out of a population of two million people assigned "female" at birth.
There's also a good chance that birth control reduces the risk of ovarian cancer
Ovarian cancer is less common than endometrial cancer, which means that studies on it often contain fewer people. However, even with less data, most studies on this topic find that taking oral contraceptives for any length of time is associated with a significantly lowered risk for ovarian cancer:
- For the general public, the risk was decreased by about 15% overall. However, for women with BRCA1 or BRCA2 genes, that risk reduction was anywhere from 40% to 80%.
- In a meta-analysis of over 4,000 ovarian cancer cases broken down by how "aggressive" they are, oral contraceptives had a larger reduction in risk of “rapidly fatal” ovarian cancer cases — close to a 30% reduction in the general public.
Evidence showing that birth control reduces the risk of colorectal cancer is weak and outdated
Colorectal cancer sometimes appears on lists of the different types of cancers that birth control could impact:
- This is supported by a meta-analysis that included over 15,000 cases of colorectal cancer over the last few decades which found that oral contraceptives were associated with an 18% reduction of colorectal cancer risk, with a maximum benefit coming from about 3.5 years of oral contraceptive use.
- The majority of studies on this topic in recent years (using new formulations with lower doses) failed to find any such relationship.
Does the type of birth control impact cancer risk?
As we touched on earlier, the bulk of the research in this area is concentrated around the pill. But we’ve seen a rise in use of progestin-only birth control methods in the last few years, including the minipill, implants, and hormonal IUDs — which might not come with the same cancer risks and benefits as combined oral contraceptives.
Since many of the theories about how hormonal birth control can lead to cancer center around estrogen’s role in encouraging cells to divide, the idea is that combined contraceptives with lower doses of synthetic estrogens might carry less risk. Although there’s not enough data yet to say one way or another, some early studies indicate that progestin-only contraception might also carry a similar increased risk for breast and cervical cancer. More research is needed to compare the potential impact of different types of birth control pills or other forms of contraception on cancer risk.
What are the other benefits and risks associated with birth control?
Many people with ovaries take the pill for its stated benefit: giving us control over when (if ever) we decide to become pregnant. However, over the years, many people have decided to take the pill for its other health benefits — either in addition to or regardless of its pregnancy-preventing abilities. These benefits include:
- Reduced period pain and/or bleeding
- Might reduce ovarian cysts
- Menstrual cycle regulation
- Reduced acne
- Reduced endometriosis symptoms
On the other hand, there are also potential risks to be aware of when considering the pill:
- Increased risk of blood clots
- Increased risk of heart disease
- Increased risk of stroke
- Unwanted side effects
The bottom line on birth control and health risks is this: Whether you decide that the benefits outweigh the risks — or the risks outweigh the benefits — will come down to a combination of your underlying health concerns, other risk factors and your personal preferences. If you’re concerned about the risks that come with different birth control options, discuss them with your doctor. Although no birth control method is perfect, your healthcare practitioner can take the time to help you find the best option for you.
This article was medically reviewed by Dr. Eva Marie Luo, MD, MBA, OB-GYN at Beth Israel Deaconess Medical Center and Clinical Lead for Value at the Center for Healthcare Delivery Science at Beth Israel Deaconess Medical Center.