An IUS (intrauterine system) is a small, T-shaped plastic device placed inside the uterus that slowly releases a low dose of a progestogen hormone to prevent pregnancy. It’s one of the most effective contraceptive methods available, with a failure rate of just 0.2% in the first year of use. The IUS is sometimes called a “hormonal coil,” and it differs from the copper IUD (intrauterine device), which contains no hormones.
How an IUS Works
The hormone released by an IUS is levonorgestrel, a synthetic form of progesterone. Its primary contraceptive effect comes from thickening the mucus at the entrance to the cervix, creating a barrier that sperm struggle to pass through. The hormone also thins the lining of the uterus over time, making it less receptive to a fertilized egg. Some users may have ovulation suppressed as well, though this isn’t the main mechanism.
Because the hormone acts locally inside the uterus rather than circulating through your entire body at high levels, the systemic side effects tend to be milder than those from oral contraceptive pills.
Available Types and How Long They Last
Several IUS brands are available, and they differ mainly in how much hormone they release and how long they can stay in place:
- Mirena: approved for up to 8 years for contraception, or 5 years when used to treat heavy periods
- Liletta: also approved for up to 8 years
- Kyleena: approved for up to 5 years, with a slightly lower hormone dose
- Skyla: approved for up to 3 years, the smallest device with the lowest dose
The smaller, lower-dose options like Kyleena and Skyla were designed partly with younger users or those who haven’t had children in mind, since the smaller frame can be easier to insert.
How Effective It Is
The IUS is among the most reliable forms of contraception. CDC data shows a 0.2% unintended pregnancy rate in the first year of use, both with typical and perfect use. That means the numbers are identical because there’s nothing for the user to remember or do correctly each day. For comparison, the copper IUD has a typical-use failure rate of 0.8%, and oral contraceptive pills fail at much higher rates with typical use because of missed doses.
What Insertion Feels Like
Getting an IUS placed takes only a few minutes in a clinic. Before insertion, your provider will do a pelvic exam to check the size and position of your uterus and to rule out any active infections. If you haven’t been recently screened for sexually transmitted infections, that testing can happen at the same appointment without delaying placement.
The insertion itself involves passing the device through the cervix, which can cause cramping that ranges from mild to quite intense. Pain experiences vary widely. Current guidelines recommend that providers discuss pain management options before the procedure. A local anesthetic (lidocaine), given either as an injection near the cervix or applied as a topical gel, may help reduce pain during placement. A medication called misoprostol, once commonly given beforehand to soften the cervix, is no longer recommended for routine use because evidence shows it doesn’t meaningfully reduce pain or improve the process.
Cramping and spotting in the days after insertion are normal. Most people can return to regular activities the same day or the next.
Changes to Your Period
One of the most noticeable effects of an IUS is lighter periods. As the hormone thins the uterine lining, your body shifts from its normal menstrual cycling to a much less active state. During this transition, irregular bleeding and spotting are common, particularly in the first three to six months.
Over time, periods typically become much lighter. Some users stop having periods altogether. In a study of over 1,800 continuous IUS users, about 5% had no periods at three months, 15% at six months, and 15% at 12 months. This isn’t harmful. It simply reflects the thinned uterine lining having very little to shed each month.
Treating Heavy Periods
The IUS isn’t only used for contraception. It’s also a first-line treatment for heavy menstrual bleeding, and for many people it works better than oral medications. Clinical trials have shown that the IUS reduces menstrual blood loss by roughly 85 to 90% within six months, compared to reductions of around 40 to 60% with various pill-based treatments. By 12 months, that advantage held steady, with the IUS maintaining an 83 to 87% reduction in bleeding. For people dealing with heavy periods that disrupt daily life, the IUS can be a significant improvement without requiring surgery.
Possible Side Effects and Risks
Common side effects in the first few months include irregular spotting, breast tenderness, headaches, and mood changes. For most users, these settle as the body adjusts. Acne is another reported side effect, particularly with lower-dose devices.
Serious complications are rare. Uterine perforation, where the device pushes through the uterine wall, occurs at a rate of roughly 1 to 4 per 1,000 insertions. Expulsion, where the IUS partially or fully slips out of place, is also uncommon but more likely in the first few months after insertion, especially during periods.
To catch any issues early, it’s recommended that you check for the device’s strings once a month. You can do this by washing your hands, squatting or placing one foot on the edge of a bathtub, and reaching your middle finger to the top of the vagina. Your cervix feels like the tip of your nose. Running your fingertip across it, you should feel thin threads. If you can’t find them, or if you feel hard plastic, contact your provider to check that the device is still in the correct position.
Who Shouldn’t Use an IUS
Most people can safely use an IUS, but there are some exceptions. You shouldn’t have one placed if you have a current pelvic infection, unexplained vaginal bleeding that hasn’t been evaluated, cervical or uterine cancer, or certain uterine abnormalities that would distort the space where the device sits. These are classified as absolute contraindications in CDC eligibility guidelines, meaning the health risks outweigh any benefit.
For conditions like a history of breast cancer, eligibility depends on how recent the diagnosis was and other individual factors. Your provider can walk through the specific criteria that apply to your situation.
Fertility After Removal
Fertility returns almost immediately after an IUS is removed. You can try to conceive the very first month. A 2018 review of studies found that contraceptive use, regardless of how long the device was in place, does not negatively affect the ability to get pregnant or delay fertility. Your baseline fertility will generally be whatever was typical for you before the IUS was inserted, adjusted for any age-related changes in the meantime.