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An IUD — not to be confused with an IED — is a T-shaped birth control device that gets inserted into your uterus and prevents pregnancy by releasing small amounts of copper or hormones into your reproductive system.

Besides being 99 percent effective at preventing pregnancy, IUDs are widely thought to make periods lighter. But all bodies are different, and your body’s reaction to an IUD may vary depending on which type you use.

If the thought of lighter periods makes you feel like frolicking down the street in bright white pants at any given time, read on.

There are two types of IUDs: copper and hormonal.

Copper IUD

A copper IUD works by preventing sperm from getting to and fertilizing an egg. And if an egg does somehow get fertilized, the copper IUD keeps it from attaching to the uterine lining.

But some people actually have longer and heavier periods with a copper IUD, especially if they switch from hormonal birth control.

Other potential (but temporary) side effects of a copper IUD include:

  • irregular periods
  • cramping
  • lower back pain
  • spotting or bleeding between periods

Most side effects are temporary and go away within 2 to 3 months of implantation.

Paragard is the only brand of copper IUD available in the United States.

Hormonal IUDs

A hormonal IUD releases levonorgestrel, a manufactured form of the hormone progesterone, into your uterus.

Levonorgestrel helps prevent pregnancies by:

  • Preventing ovulation. Levonorgestrel sometimes prevents your ovaries from releasing eggs, but this isn’t its main function. Hormonal IUDs are primarily meant to thin your uterine lining (aka endometrium) and thicken your cervical mucus.
  • Thinning the uterine lining. Usually, your uterine lining must thicken to properly receive a fertilized egg. If the lining is too thin, the egg can’t attach.
  • Thickening cervical mucus. Much like Artax’s quicksand demise in “The NeverEnding Story” (it will always be too soon), thick cervical mucus makes it nearly impossible for sperm to get to the egg.

A quick 7th grade health class reminder of what your period actually is:

It’s when your uterine lining evades pregnancy and sheds away, exclaiming “Buh-bye!” on its way out of your vagina.

Hormonal IUDs can be used to alleviate menstrual symptoms like heavy bleeding or long periods because levonorgestrel thins your uterine lining. When there’s less lining to flow out, you may have lighter and/or shorter periods.

Currently, four types of hormonal IUDs exist in the United States. They all use the same hormone but last from 3 to 7 years, depending on how much levonorgestrel they contain.

The higher the amount of levonorgestrel, the longer the IUD will last and the lighter your period will most likely be. For some women, periods may go away completely while using a hormonal IUD. Normal fertility usually returns soon after an IUD is removed.

The four brands of hormonal IUD are:

If you’re trying to figure out if an IUD will banish your periods to the invisible land of lost hair ties and socks, it really depends on how heavy your period naturally is.

A 2016 study found that after a year of using the Mirena IUD, 21 percent of women who had lighter, shorter periods without birth control saw their periods stop altogether, while 5 percent of women with naturally heavy periods saw the same result.

A copper IUD may make you crampier and your period heavier and longer, but these symptoms usually go away after a few months.

A hormonal IUD may make your period lighter and shorter or nonexistent for as long as you’re using it. Skyla, Kyleena, Liletta, and Mirena are the big four brands you should know.

Because a copper IUD doesn’t contain hormones, it doesn’t affect your ovulation. You’ll still get regular periods, but they’ll most likely be longer and heavier for the first few months, and you may have more cramping than before.

After the 6-month mark, your periods should chill out and go back to their normal cycle and flow.

If they don’t and you’re still bleeding heavily after 6 months, consult the healthcare provider who inserted your IUD.

Everybody and every body is unique and will react to an IUD differently. It can take months for your body to fully adjust to this new form of birth control (and the hormones in it).

From insertion to the 6-month mark, your periods may be heavier or last longer than usual. About 20 percent of women using a hormonal IUD have periods that last longer than 8 days. Spotting is also common at the beginning.

After the 6-month mark, your period should become less frequent and lighter, or it could stop altogether.

Going to the gyno while on your period may sound like a nightmare (for you and the doctor), but many doctors actually prefer to insert an IUD while you’re bleeding.

Though an IUD can be inserted any time, your cervix may be more open and soft while you’re on your period.

It also ensures you’re not preggers, which is a big one, because getting an IUD when you’re pregnant can result in:

Hormonal IUDs are also immediately effective if inserted while you’re on your period. Otherwise, they can take up to a week to start working.

Copper IUDs are immediately effective whenever they’re inserted, because the copper itself prevents pregnancies.

Fun fact:

A copper IUD can also be used to prevent a pregnancy up to 5 days after unprotected sex.

If you know anyone who’s gotten an IUD — whether hormonal or copper — you’ve probably heard about some of the meh side effects that can happen right after insertion.

Dizziness, bleeding, and temporary pain are common but shouldn’t last longer than a half hour. If they do, consult your doctor.

Some women’s bodies reject the IUD, which can cause it to puncture the uterine wall. If you think this may have happened, see your doctor immediately, because the IUD will need to be removed.

While it’s incredibly uncommon, some women can become pregnant while they have an IUD, which can cause serious medical complications like infections or ectopic pregnancy. If you have an IUD and become pregnant, see a doctor ASAP.

If you start experiencing any of the following symptoms after getting an IUD, seek medical attention:

  • pain during sex
  • chills
  • fever
  • stomach pain
  • pregnancy symptoms
  • rancid-smelling vaginal discharge
  • missing a period for more than 6 weeks
  • vaginal sores
  • jaundice (yellowing of your skin or the whites of your eyes)
  • severe headaches
  • intensely heavy periods after the first 6 months

Side effects aside, once your doctor inserts your IUD, there’s nothing left for you to do.

Check the threads once a month to make sure the IUD hasn’t shifted (though if you can’t feel them, it’s likely they’ve just curled upward). Call your doctor if you have any questions.

IUDs are an extremely effective and safe form of birth control that prevents pregnancy by releasing a small amount of copper or hormones into your reproductive system.

Women with hormonal IUDs may have fewer, lighter periods, while women with copper IUDs may have heavier, longer periods for the first few months.

If you have an IUD and think you could be pregnant, see your doctor immediately. If you want to change your birth control method, talk to your doctor, who can help you transition smoothly and safely.