Officials with the American College of Obstetricians and Gynecologists said that they would carefully evaluate the new findings, but emphasized that hormonal contraceptives are for many women “among the most safe, effective and accessible options available.”

Experts noted that oral contraceptives have some benefits as well, and are associated with reductions in ovarian, endometrial and possibly colorectal cancers later in life.

Dr. Chris Zahn, A.C.O.G.’s vice president for practice activities, acknowledged a link between breast cancer risk and hormone use, but urged concerned women to consult a trusted medical provider before making changes. “It’s important that women feel confident and comfortable with their contraceptive choice,” he said.

Because risk increases with age, Dr. Weiss suggested that older women may want to consider switching to a hormone-free birth control method, like a diaphragm, an I.U.D. that does not release hormones, or condoms. “It’s not like you don’t have a choice,” she said. “Why not pursue another option?”

In a commentary accompanying the new study, which was published in the New England Journal of Medicine, David J. Hunter, a professor of epidemiology and medicine at the University of Oxford, said the new study did not find that any modern contraceptives were risk-free.

“There was a hope that the contemporary preparations would be associated with lower risk,” he said in an interview. “This is the first study with substantial data to show that’s not the case.”

Nearly 10 million American women use oral contraceptives, including about 1.5 million who rely on them for reasons other than birth control. The number of women in the United States with intrauterine devices, many of which release hormones, has grown in recent years, as has the number of women using other types of hormonal contraceptive implants.