A large-scale study published Wednesday in the New England Journal of Medicine brings more clarity to the cardiovascular disease risks caused by birth control pills, adding to previous findings from smaller studies.
Some formulations of oral contraceptives, which contain a mix of estrogen and progesterone, can double a woman’s risk of having a heart attack or stroke, according to the new research, but in absolute terms the risk is very low because young women under age 50 rarely have heart attacks or strokes.
“I would say in many ways, this is a good news story,” said Dr. Isaac Schiff, chief of obstetrics and gynecology at Massachusetts General Hospital. “This is a lengthy, large study that helps to confirm that the birth control pill is relatively safe, recognizing that no drug is 100 percent safe.”
In the study, Danish researchers followed 1.6 million reproductive-age women over a period of 15 years to determine whether birth control pills and other hormonal contraceptives raised their risk of having a stroke or heart attack. They found only combination pills were associated with an increased risk and that the risk was slightly higher with pills that contained more estrogen. Compared with women who didn’t take oral contraceptives, there was a 60 percent higher risk of stroke in those who took pills with 20 micrograms of estrogen daily, a 75 percent higher risk in those who took pills with 30 to 40 micrograms, and a 97 percent higher risk in those who took pills with 50 micrograms for at least four years.
But considering how rarely strokes and heart attacks occur in women under age 50, that added risk amounts to 1 extra heart attack and 1 extra stroke per 10,000 pill users every year, according to Dr. Diana B. Petitti, a physician and epidemiologist at Arizona State University who wrote an editorial that accompanied the study. The study was observational and couldn’t prove that the extra strokes and heart attacks were caused by birth control pills.
Schiff also pointed out that previous studies have shown benefits of oral contraceptives beyond preventing pregnancy, such as protecting against ovarian cancer and ectopic pregnancies.
Interestingly, the study didn’t find that the type of synthetic progesterone or progestins in pills made a significant difference in determining the risk of artery blood clots that lead to strokes and heart attacks, even though research published last year found that certain types of progestins raised the risk of dangerous blood clots in veins. Pills containing estrogen and the progestin drospirenone—such as Yaz, Yasmin, and Beyaz -- were up to twice as likely to be associated with blood clots in leg veins.
Certain subgroups of women, however, were more likely in the latest study to have heart attacks and strokes, including those who were over age 45 or who had high blood pressure.
“If a woman is diagnosed with hypertension,” said Petitti, “she shouldn’t be taking a combination oral contraceptive.” She should also have her blood pressure checked before starting a pill prescription and monitored regularly while she’s on it. Progestin-only pills, the injection Depo Provera, or an intrauterine device may be safer options for those with hypertension, she added.
Since heart attacks and strokes increase with age, women heading into their mid- to late 40s may also want to consider switching away from combination hormone products, which include the vaginal ring and skin patch. “To pick an age cutoff is slightly arbitrary,” Petitti said, but women are past the point of having children may want to consider a permanent option like tubal ligation or a long-term method like an IUD.
Women who are over 35, smoke, and use the pill are at the greatest risk of heart complications, she added. “They need to be informed that they’ll start getting into [the] danger zone when it comes to considering stroke and heart attack and should be urged to stop taking the pill if they continue to smoke.”