An IUD is a small, T-shaped device placed inside the uterus that prevents pregnancy with over 99% effectiveness in both typical and perfect use. That makes it one of the most reliable forms of birth control available, outperforming the pill (91% typical use), condoms (82%), and the contraceptive injection (94%). There are two types: copper and hormonal, and they work in different ways.
How a Copper IUD Prevents Pregnancy
The copper IUD (sold as Paragard in the U.S.) contains no hormones. Instead, it’s wrapped in a small amount of copper wire that continuously releases copper ions into the uterus. These ions create an environment that’s toxic to sperm, impairing their ability to move and survive. Copper also triggers a low-level inflammatory response inside the uterus, which further reduces the chances of fertilization.
Interestingly, the copper doesn’t kill sperm on contact. Research shows it takes about three to four hours for copper ions to significantly inhibit sperm motility, meaning the device works more like a hostile environment than an instant barrier. The copper also affects egg viability and makes the uterine lining less hospitable, lowering the chances that a fertilized egg could implant even if fertilization somehow occurred.
How a Hormonal IUD Prevents Pregnancy
Hormonal IUDs release a small, steady amount of a synthetic hormone called progestin directly into the uterus. This triggers several changes that work together to prevent pregnancy. The most important is thickening the cervical mucus into a dense plug that sperm can’t easily pass through. At the same time, the hormone thins the uterine lining and interferes with sperm’s ability to function normally once inside the reproductive tract.
Because the hormone is released locally rather than circulating through your entire body, the dose is much lower than what you’d get from a birth control pill. Some women still ovulate with a hormonal IUD in place, but pregnancy is prevented by those other mechanisms. The local delivery also means fewer systemic side effects for most people, though some women do notice headaches, acne, breast tenderness, or mood changes.
Available Brands and How Long They Last
Five IUDs are currently FDA-approved in the United States. They vary in type, hormone dose, and how many years they remain effective:
- Paragard (copper, no hormones): up to 12 years
- Mirena (hormonal): up to 8 years
- Liletta (hormonal): up to 8 years
- Kyleena (hormonal): up to 5 years
- Skyla (hormonal): up to 3 years
The hormonal options differ mainly in their progestin dose and physical size. Kyleena and Skyla are slightly smaller, which can make insertion easier for women who haven’t been pregnant before. All of them can be removed earlier than their expiration date if you want to stop using them or switch methods.
Beyond Birth Control: Treating Heavy Periods
Hormonal IUDs are also FDA-approved for treating heavy menstrual bleeding. Because progestin thins the uterine lining, it directly reduces the amount of tissue that sheds each month. Many women with heavy periods see a significant decrease in blood flow and cramping after getting a hormonal IUD. Some stop having periods altogether after several months of use.
This makes hormonal IUDs a common alternative to medications or surgery for women dealing with heavy bleeding. The effect lasts as long as the device is in place, so it’s a low-maintenance option compared to taking daily pills.
Emergency Contraception
The copper IUD doubles as one of the most effective forms of emergency contraception. It can be inserted up to five days after unprotected sex to prevent pregnancy. If the timing of ovulation can be estimated, it may even be placed more than five days after intercourse, as long as it goes in within five days of ovulation. No pill-based emergency contraceptive matches its effectiveness, and once it’s in place, it continues working as long-term birth control.
Risks and Complications
Serious complications from IUDs are rare. Uterine perforation, where the device pushes through the wall of the uterus, occurs in roughly 1 to 4 out of every 1,000 insertions. The risk is higher for women who get an IUD placed soon after giving birth, particularly in the first six weeks postpartum, where perforation rates increase several-fold compared to women who aren’t recently postpartum. Breastfeeding also modestly raises the risk.
Expulsion, where the IUD partially or fully slips out of place, is another possibility, most commonly in the first few months after insertion. You can check that your IUD is still in position by feeling for the thin strings that hang through the cervix. If you can’t find them, or if you feel hard plastic, contact your provider.
The most common non-serious side effects depend on the type. Copper IUDs tend to make periods heavier and crampier, especially in the first few months. Hormonal IUDs typically cause irregular spotting initially, which usually decreases over time as periods get lighter.
Fertility After Removal
Your ability to get pregnant returns almost immediately after an IUD is removed, regardless of which type you had or how long it was in place. You can start trying to conceive the very first month. A large review covering nearly 15,000 women found that prior contraceptive use, including IUDs, doesn’t delay fertility or reduce the ability to conceive. Among the women studied, 83% became pregnant within 12 months of stopping their contraceptive method.
Those conception timelines are roughly in line with normal fertility rates. For women under 35, there’s about a 20% chance of conceiving each cycle, with 60% pregnant by six months and 85 to 90% by one year. Over 35, the monthly odds drop to 10 to 15%, and over 40, to about 5%. The IUD itself doesn’t change these numbers. Age is the primary factor.