Nearly two-thirds of American women of childbearing age use some form of birth control, according to the Centers for Disease Control and Prevention. Millions use hormone-based methods, like birth control pills, intrauterine devices (IUDs), rings, implants, injections, and patches.

While the specifics differ between methods, hormonal contraception generally works by stopping ovulation and/or altering the uterus or cervix to prevent pregnancy. And it is effective: when used correctly, these methods have less than a 1% chance of resulting in pregnancy in a year.

However, hormonal birth control has a bad reputation. Many women worry about how hormones like estrogen and progestin may impact their short- and long-term health, to the point where some opt for less effective barrier methods instead. A survey found about a third of women of reproductive age not currently using contraception avoid it due to concerns over side effects.

“They’re wonderful products, yet we maintain a cultural belief that hormones are somehow bad,” says Dr. Jeffrey Jensen, director of the Women’s Health Research Unit at Oregon Health and Science University. “That’s, in my opinion, simply not true.” (Jensen has received consulting fees from pharmaceutical companies that make contraceptive products.)

Here is what research says about hormonal birth control and health.

The side effects of birth control

In the KFF survey, around a third of women using contraception said they currently experienced side effects such as weight gain, headaches, bloating, nausea, mood changes, and menstrual changes. While these issues are usually not severe enough to be medically concerning, they can significantly impact quality of life. Studies show many women stop using birth control due to side effects.

However, Jensen notes birth control sometimes brings positive changes too. It can lessen issues like acne, heavy or irregular periods, and menstrual cramps.

Is birth control linked to cancer?

Research suggests women using hormonal contraception have a slightly higher risk of breast and cervical cancers. However, that elevated risk seems temporary, dropping after stopping birth control.

Studies also indicate hormonal birth control lowers the risk of other cancers like ovarian, endometrial, and colorectal cancers—and those protective benefits seem to last for decades even after stopping use.

When it comes to cancer, the pros and cons effectively cancel out, says Lisa Iversen, an advanced research fellow at the University of Aberdeen in Scotland. In 2017, she co-authored a meta-analysis on lifetime cancer risks for birth control pill users which analyzed decades of health data from over 46,000 women. “Overall,” she says, “we found a neutral balance when comparing risks and benefits.”

Still, Iversen says it’s always smart to speak with a physician about your specific personal and family risk factors before starting a new prescription.

Does birth control cause cardiovascular issues?

Birth control pills containing estrogen have been linked to slightly higher risks of blood clots and strokes. But some researchers question the strength of association between contraception and cardiovascular problems. Authors of a review of previously published research concluded little high-quality evidence proves birth control causes serious health issues, including cardiovascular complications and cancer. In fact, research suggests birth control pills may actually decrease a woman’s risk of developing heart disease or dying prematurely.

Those with specific risk factors for stroke or blood clots should speak to their physicians before choosing a method. But overall, it’s important to keep potential drawbacks in perspective, says Dr. Elizabeth Kinsey, a complex family planning fellow at the University of California, San Francisco’s Bixby Center for Global Reproductive Health. , particularly given the U.S.’s , she notes.

Further, Kinsey says, conditions like cancer and stroke are among women of childbearing age. So even if contraception slightly increases a woman’s risk of developing them, her overall risk still remains low.

What about IUDs and other forms of hormonal birth control?

. The Dalkon Shield, a type of IUD popular in the U.S. in the 1970s, was eventually linked to health issues including infections and pelvic inflammatory disease, causing some lingering concerns about these devices. However, modern IUDs are designed differently and .

Hormonal IUDs available in the U.S. also do not contain estrogen, only progestin, which should minimize concern about clots and stroke, Jensen says. Studies on IUDs and cancer suggest a mix of pros and cons, similar to those associated with birth control pills: , balanced by reductions in the risk of and .

also analyzed the hormone used in the birth control shot, medroxyprogesterone acetate. It found prolonged medroxyprogesterone acetate use may be associated with an increased risk of developing a type of slow-growing (and usually benign) tumor in the membranes around the brain and spinal cord. However, hormones used in IUDs were not associated with that risk, the study found.

Kinsey says she’d like to see more research on lesser-used forms like rings and patches. But based on currently available science, Jensen says most people don’t have huge reason to worry about using hormonal contraception, although individual risks are worth discussing with a doctor.

“For the most part,” he says, “we should be looking [at the science] and celebrating.”