Some of us ladies think we might want to become mothers someday in the distant future. Others have put our baby-making days behind us. For any woman who wants to keep her baby oven empty, whatever the reason, a long-term birth control option such as an IUD (intrauterine device) is an excellent option. Unlike the Pill, which is highly effective but only if you remember to take it (hangovers and time zone changes be damned), IUDs are 99% effective and once they’re in, you don’t have to give them much thought … for years.

So how exactly does an IUD work? First, let’s go over a little IUD 101: There are several different kinds, both hormonal and non-hormonal. “One that’s gained in popularity in Skyla — it’s a three-year reversible IUD, meaning it’s effective up to three years, but it can be reversed and removed at any time or it can be replaced after three years,” Alyssa Dweck, an OB-GYN at the Mount Kisco Medical Group in NY, and co-author of V is for Vagina, told YouBeauty.

Skyla is a hormonal IUD that releases a small amount of progestin into the uterus at a slow and continuous rate. “It works by thickening the cervical mucus, which inhibits sperm movement and reduces the survival of sperm, and it thins the lining the uterus.” Skyla is approved for both women who have kids and those who haven’t had children yet.

Another popular hormonal IUD is Mirena. Like Skyla, is also releases progestin and can be removed and reversed at any time, but Mirena can last up to five years before needing to be replaced. “Mirena has another indication, which is incredibly important — it’s not only an effective birth control, but it also helps with heavy menstrual flow,” says Dweck. In fact, it’s FDA-approved to treat heavy periods and can lead to very light or zero monthly bleeding at all.

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ParaGard is a non-hormonal IUD. It works by releasing copper into the uterine lining, which creates an inflammatory reaction that inhibits sperm movement and egg fertilization. It may also prevent implantation. The device is reversible and is good for up to 10 years. That said, ParaGard can make periods heavier and longer and cause more cramps, notes Dweck, so it may be a better option for women who aren’t able to use hormonal IUDs and are looking for long-lasting, highly effective contraception.

However, not everyone is a candidate for an IUD. The birth control method can’t be used if you’re pregnant, which likely goes without saying, or if you’ve had a serious pelvic infection, such as pelvic inflammatory disease that’s recent or untreated. Women who have progesterone-receptive-positive breast cancer also aren’t candidates for hormonal IUDs.

If your gyno gives you the green light to get one, you can have an IUD inserted in the doctor’s office. To make insertion more comfortable, Dweck recommends taking an over-the-counter pain reliever beforehand and having the IUD placed during the very end of your period. “Insertion may be a little bit easier then,” she says. “And it’s effective right away.”

You’ll also need to occasionally check the little threads that are attached to the IUD to make sure it’s still in place, which your gynecologist can teach you how to do. It’s also worth noting that IUDs don’t provide STD protection, so you’ll still need to use condoms if you’re not in a monogamous relationship.

Planned Parenthood notes that IUDs are the most inexpensive long-term and reversible forms of birth control available. Talk to your gynecologist to find out if an IUD is right for you.

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