But the overall increased risk was small, amounting to one extra case of breast cancer among 7,700 women using such contraceptives per year.
The study is based on health records of 1.8 million women in Denmark.
These results sound scary at first.
The study, which followed 1.8 million Danish women for more than a decade, upends widely held assumptions about modern contraceptives for younger generations of women.
Women who now use or recently used hormone-based contraception face a 20 percent higher risk of breast cancer, although the overall risk for most women is relatively low, a new study of 1.8 million women in Denmark has concluded. And for those who take the drugs for five years or more, the risk will persist for as long as five years after they stop, she said.
Women who used an intrauterine device that releases only progestin also faced a 21 per cent increase in risk, compared with non-users, the study found.
Third-generation contraceptive pills are displayed on January 2, 2013, in Lille, in northern France.
A new study is showing the link between the use of birth control to increased risk of breast cancer.
For now, Morch said, even with the newer pharmaceuticals, women whose families have a strong history of breast cancer or heart disease may want to consider using other methods of birth control, such as employing condoms or spermicidal devices.
"It's a 20 percent increase in risk, but the absolute risk is very low", Dr. Joann Manson said. "The range of risks we're talking about here is much much smaller", she said.
It's a disappointment to doctors who had hoped that lower doses of hormones in both oral and non-pill contraceptives might be safer than older birth control pills. Dr. Charles A. Leath, a gynecologic oncologist at the University of Alabama at Birmingham, said that while this pathway was plausible, it was far from certain.
For some perspective, about 252,710 American women were diagnosed with breast cancer in 2017, according to estimates from the National Institutes of Health; 12.4 percent of women will hear the diagnosis at some point in their lives.
The increase in breast cancer cases associated with hormones was also small because young women are at low risk to begin with. "[Contraceptives] also brings benefits, and we should not forget them". "This is the first study with substantial data to show that's not the case".
Of course, finding a safe and effective form of birth control is more than just a personal concern.
The study of nearly 2 million women in Denmark looked at women using birth control methods such as the pill, NuvaRing, or implants. "As with any medical intervention, hormonal contraception is associated with specific health risks".
However, hormonal birth control does lower the risk of other cancers, including ovarian cancer and endometrial cancer, and it may lower the risk of colon cancer.
Two types of birth control pills are sold in the USA - one that combines synthetic versions of the hormones estrogen and progesterone, and the "minipill" that only delivers progestin, a synthetic formulation of progesterone. Risk seemed to increase the longer the contraceptive was used.
The new study looked at all women in Denmark ages 15 to 49 who had not had cancer, clots in their veins, or treatment for infertility.
IUDs infused with hormones also appear to pose a risk, Morch said, so "so there's a lot of things to take into account when deciding what type of contraception to use". But he suggested doctors take time to discuss the pros and cons of different types of contraception with their patients, and that they be frank about the potential risks, suggesting women reassess hormone use as they age.