A coil is a small, T-shaped device placed inside the uterus to prevent pregnancy. It’s one of the most effective forms of reversible contraception available, with a failure rate below 1% per year. The medical term is intrauterine device, or IUD, but “coil” remains the common name in many countries. Two main types exist: a copper coil that contains no hormones and a hormonal coil that releases a low dose of progestin.
Copper Coil vs. Hormonal Coil
The copper coil is wrapped in copper wire and contains no hormones at all. It works by releasing copper ions into the uterus, which interfere with sperm movement and function, preventing sperm from reaching and fertilizing an egg. The copper version is approved for up to 10 years of continuous use, making it the longest-lasting reversible contraceptive option. It’s also the only non-hormonal IUD on the market.
The hormonal coil releases a small, steady amount of progestin directly into the uterus. This thickens the cervical mucus so sperm can’t easily pass through, and it thins the uterine lining. Several hormonal options are available, each approved for a different duration: Mirena lasts up to eight years, Liletta up to six, Kyleena up to five, and Skyla up to three. The differences come down to the amount of hormone released and the physical size of the device, which can matter if you have a smaller uterus.
How Effective Is a Coil?
IUDs are among the most reliable contraceptives because they don’t depend on you remembering to take or use anything. The hormonal coil has a typical-use failure rate of just 0.2% in the first year, meaning only 2 in 1,000 users become pregnant. The copper coil’s typical-use failure rate is 0.8%, or about 8 in 1,000. For comparison, the pill has a typical-use failure rate of 8%, and male condoms sit at about 15%. The only methods more effective than an IUD are surgical sterilization procedures.
“Typical use” and “perfect use” numbers are nearly identical for coils because there’s nothing for the user to do wrong once the device is in place. With the pill, the gap between perfect use (0.3%) and typical use (8%) reflects missed doses and timing errors. That gap essentially disappears with a coil.
What Insertion Feels Like
Getting a coil placed is a routine procedure that takes 5 to 15 minutes. A healthcare provider performs a pelvic exam, cleans the cervix with an antiseptic solution, then inserts the device through the cervical opening into the uterus. Short strings attached to the device are trimmed so they hang just inside the vagina, allowing you to check the coil is still in place. An ultrasound or manual exam may be done afterward to confirm correct positioning.
Pain during insertion varies widely from person to person. Some feel only mild cramping, while others find it intensely uncomfortable. Current CDC guidelines recommend that providers discuss pain management options beforehand and create a plan based on your preference. A local anesthetic, applied as an injection near the cervix or as a topical gel, can help reduce pain during placement. Taking an over-the-counter pain reliever before your appointment is another common approach. The sharp discomfort typically lasts only seconds, though cramping can continue for a few hours or days afterward.
Side Effects of the Copper Coil
Heavier periods and more cramping are the most common complaints with the copper coil. In one study of over 600 users, about two-thirds reported increased menstrual blood loss in the first nine weeks after insertion, and 38% reported more pain during their period than before. These side effects do improve with time. By the fourth period (roughly 10 months in), the percentage reporting heavier bleeding dropped from 68% to about 49%, and pain reports decreased as well. The average number of bleeding days also shortened slightly, from six days to about five and a half.
That said, the copper coil will not stop your periods or make them lighter. If you already have heavy, painful periods, a copper coil may not be the best fit. The side effects are enough to prompt some users to have the device removed early, though the majority of women who make it through the initial adjustment period find the bleeding and cramping settle to manageable levels.
Side Effects of the Hormonal Coil
The hormonal coil tends to have the opposite effect on periods. Because it thins the uterine lining, most users experience lighter bleeding over time. About 20% of people using the Mirena stop having periods entirely after one year. For many, this is a welcome benefit rather than a side effect.
Other reported side effects include headaches, acne, breast tenderness, mood changes, and pelvic pain or cramping. Irregular spotting is common in the first three months but usually improves. Because the hormone acts primarily in the uterus rather than circulating through the entire body at high levels, systemic side effects tend to be milder than those seen with the pill or hormonal injections, though some people are more sensitive than others.
Risks and Complications
Serious complications from a coil are uncommon. The two main risks are perforation and expulsion. Perforation, where the device pushes through the uterine wall, has a cumulative incidence of about 0.2% at one year and 0.6% at five years. It’s rare, but if it happens, the coil needs to be removed, sometimes surgically. Expulsion, where the coil partially or fully slips out of position, is more common, occurring in roughly 2.3% of users within the first year and nearly 5% by five years. You can check for expulsion by feeling for the strings, and if the device shifts, it needs to be repositioned or replaced.
There is a small increase in infection risk in the weeks immediately after insertion, but this is related to the placement procedure itself rather than the device. After that initial window, coils do not increase your risk of pelvic infections.
Who Can and Can’t Use a Coil
Most people with a uterus can safely use a coil, including those who have never been pregnant and teenagers. However, certain conditions make IUDs unsuitable. You should not have a coil placed if you are currently pregnant, have an active pelvic infection, have unexplained vaginal bleeding that hasn’t been evaluated, or have a uterine cavity with significant structural distortion. Current cervical or endometrial cancer and pelvic tuberculosis are also contraindications. Your provider will review your medical history to confirm a coil is appropriate for you.
Removal and Return to Fertility
A coil can be removed at any time by a healthcare provider, and the process is typically quicker and less uncomfortable than insertion. The provider grasps the strings and gently pulls the device out through the cervix. Fertility returns almost immediately, because most IUDs do not suppress ovulation in the first place. You can potentially become pregnant right away after removal, regardless of whether you had a copper or hormonal coil.
If you had a hormonal coil, your periods may take a few months to return to their pre-IUD pattern, especially if your bleeding had become very light or stopped altogether. This adjustment period reflects your uterine lining rebuilding, not a delay in fertility itself.