How does birth control work?
There are basically two types of birth control pills, synthetic forms of the hormones progesterone and estrogen, which can be close to 100 percent effective at preventing pregnancy if used correctly. One type contains the female sex hormone progesterone and the other type contain a combination of estrogen and progesterone, explains Jill Rabin, MD, co-chief of the division of ambulatory care and Women’s Health Programs-PCAP Services at Northwell Health in New Hyde Park, NY. The hormones work in different ways to prevent pregnancy. “Progesterone thickens the cervical mucus, making it difficult for sperm to penetrate, and it also makes the Fallopian tubes move slower so the egg and sperm don’t get together quite as efficiently,” she says. “It also makes the uterine lining hostile to implantation.” A fertilized egg can’t implant in a thin lining—it needs a soft cushy place to implant. Estrogen inhibits ovulation by suppressing the hormones responsible for ovulation. “If you interrupt this cycle, an egg won’t come out and a steady state of estrogen interrupts it,” Dr. Rabin says. Neither type of birth control pills protect against sexually transmitted diseases, which are on the rise (are you at risk for STDs?).
Are there any women who can’t take combined birth control pills?
“A lot of people can’t take estrogen,” says Dr. Rabin, who is based in New Hyde Park, NY. The list includes women with a personal history of a blood clots, breast cancer, or heart disease, and smokers. Progesterone alone is safer in some women. These are the silent signs you’re on the wrong birth control.