We were curious—and thought you might be too—about how contraception really works, so we looked into how eight of the more complicated forms of birth control (read: not physical forms of protection like condoms or diaphragms) work their magic. ~Science!~
The Non-Hormonal IUD
Opted to go hormone-free with your IUD? Your copper IUD (known as Paragard) more or less acts as a spermicide, negatively impacting swimmers’ ability to move and reach your egg, which has to happen in order for you to get preggers.
In essence, the copper IUD creates an inflammatory environment in your uterus that prevents implantation, explains Brian Levine, M.D., founding partner and practice director of the fertility clinic CCRM New York. Once in place, your copper IUD does its job diligently for up to 10 years without you ever having to think twice. IUDs in general are considered a really safe bet—they're more than 99 percent effective.
A Hormonal IUD
How do they work? They contain a synthetic hormone called progestin that thickens your cervical mucus, more or less making it impenetrable, thereby preventing pregnancy, explains David Ryley, M.D. a reproductive endocrinologist at Boston IVF (read: No sperm getting through here!).
Progestin also thins the lining of the uterus and could stop your body from ovulating (AKA releasing an egg), he says. And if you don’t ovulate? Well, then it’s pretty tough to get pregnant.
Depending on which brand you choose, hormonal IUDs stay in place and work effectively for three to five years.
Combined Oral Contraceptives
The combination pill is your classic birth control pill and it’s a mix of both estrogen and progestin. How it works: by preventing the release of two other hormones (follicle-stimulating hormone and luteinizing hormone) that cause ovulation, explains Dr. Ryley.
When taken every day (key part here!), your ovaries don’t release eggs, your cervical mucus thickens, and the lining of your uterus thins out—all factors that keep you baby-free. Birth control pills are also over 99 percent effective, but you have to use them according to your doc's direction, otherwise they're closer to 91 percent effective.
The Progestin-Only Pill
Sometimes called the mini-pill, the progestin-only pill only has one hormone in it: progestin. In this case, progestin thickens up your cervical mucus, again, to prevent sperm from swimming up the uterus, says Dr. Levine.
But since the combo of estrogen and progestin (versus just progestin alone) is more effective at suppressing ovulation, you *might* still ovulate on the mini-pill.
To be effective, you also have to take it at the same time every day, says Dr. Levine.
The Hormonal Vaginal Contraceptive Ring
The ring is pretty darn similar to the pill in terms of how it works. It contains both progestin and estrogen and prevents ovulation. It’s just that instead of popping a pill, this device is inserted into your vagina and left in place for three weeks, says Dr. Levine. From there? The hormones in the ring are absorbed into your bloodstream.
There's a bit more human error at work with this method as well, meaning if it's used perfectly it's 99 percent effective, but it's actually closer to 91 percent.
The Birth Control Shot
“The shot is a three-month dose of a progestin,” says Dr. Levine. And while the amount of progestin in the mini-pill usually isn’t enough to suppress ovulation, the shot comes with a much higher dose, so it can keep you from ovulating, he says.
It also makes cervical mucus thick—that same environment that sperm really can’t work well in, he says.
The shot is 99 percent effective if you get your shot on time every time, but any wiggle room with your dates and it's actually closer to 94 percent.
This thin rod about the size of a matchstick goes under the skin of your upper arm and, like the shot, it contains a hefty dose of progestin that’s released over the course of three years, says Dr. Levine.
Like other forms of BC, it also makes cervical mucus thick, and it thins the lining of the uterus to stop sperm in their tracks and fend off possible pregnancies.
You also can't personally mess this one up—it's in your arm! So it's 99 percent effective.
You wear this skin patch on your lower stomach area, butt, or upper body for three weeks in a row with a week off, then you put a new patch on for three weeks and repeat. How it does its job? By releasing both progestin and estrogen into your bloodstream, stopping ovulation, and cooking up that thicker cervical mucus that sperm can’t swim in.
Similar to the pill and the ring, this one is only 99 percent effective if you use it flawlessly, otherwise you're looking at stats closer to 91 percent.
This article originally appeared on Cosmopolitan.com. Minor edits have been made by the Cosmo.ph editors.