Hormonal IUDs are slightly more effective than the copper IUD at preventing pregnancy, but the difference is small. All IUDs are over 99% effective in the first year, placing them among the most reliable contraceptive methods available. The real differences show up when you compare specific brands and look at how long each device lasts.
Failure Rates by Brand
Four hormonal IUDs and one copper IUD are available in the United States. Each releases a different amount of the hormone levonorgestrel (or, in the case of Paragard, no hormone at all), and their first-year failure rates reflect those differences:
- Liletta: 0.15 pregnancies per 100 users in the first year
- Kyleena: 0.16 per 100
- Mirena: 0.2 per 100
- Skyla: 0.41 per 100
- Paragard (copper): approximately 0.6 to 0.8 per 100
To put these numbers in context, the pill, patch, and ring have a typical-use failure rate of about 9 per 100 users per year. Even Skyla, the least effective IUD on this list, is roughly 20 times more reliable than those methods. The gap between the most and least effective IUD is real but narrow: fewer than 1 extra pregnancy per 100 users over a full year.
How Each Type Prevents Pregnancy
Hormonal IUDs release levonorgestrel directly into the uterus. This thins the uterine lining, thickens cervical mucus so sperm can’t travel through it easily, and in some cases partially suppresses ovulation. The combination of these effects is what gives hormonal IUDs their edge in failure rates.
The copper IUD works without hormones. Copper ions create a localized inflammatory response inside the uterus that is toxic to sperm, impairing their ability to move and survive. It starts working immediately after insertion, which is one reason it doubles as the most effective form of emergency contraception. In studies involving 960 copper IUD insertions for emergency use, the failure rate was just 0.1%, compared to 1.5% for emergency contraceptive pills.
How Long Each IUD Lasts
Approved duration varies significantly by device. Mirena and Kyleena are approved for 5 years. Skyla is approved for 3 years. Liletta was initially approved for 3 years, though its approval has since been extended. Paragard is approved for 10 years, giving it the longest official lifespan of any IUD.
Clinical evidence supports even longer use for some devices. Research involving the Paragard found zero pregnancies when use was extended to 12 years, and a professional guideline from the Society of Family Planning recommends that people over 30 at the time of insertion can consider using it for 12 to 20 years, or even until menopause. For the 52-mg hormonal IUD (Mirena and Liletta’s class), studies show it remains effective for at least 7 years, and Canada approved it for up to 8 years as of early 2024.
This matters for overall effectiveness because the longer a device stays in place, the fewer times you go through the process of removal and reinsertion, each of which introduces a brief window of vulnerability.
Expulsion and What Affects It
An IUD can only work if it stays in place. Expulsion, where the device partially or fully slips out, is the main way real-world effectiveness drops below the clinical ideal. The 36-month cumulative expulsion rate is about 10 per 100 users regardless of IUD type. Hormonal and copper IUDs were expelled at nearly identical rates in a large study: 10.1 per 100 for hormonal versus 10.7 per 100 for copper.
Age is the strongest predictor. Teens under 20 had a 36-month expulsion rate of 18.8 per 100, roughly double the 9.3 per 100 rate for users 20 and older. Having given birth previously also raised expulsion risk (11.4 per 100 versus 8.4 for people who had never delivered). Higher body weight plays a role too: in a study of young nulliparous users, each categorical increase in BMI percentile was associated with roughly 3 to 5 times higher odds of expulsion compared to those with an average BMI.
Even with expulsion factored in, IUDs remain more reliable than shorter-acting methods. The risk of discontinuing the pill or the injection is higher than the risk of an IUD falling out of place.
Ectopic Pregnancy Risk
A common concern is whether IUDs increase the risk of ectopic pregnancy, where a fertilized egg implants outside the uterus. A meta-analysis of over 21,000 women found that current IUD use does not increase the overall risk of ectopic pregnancy compared to women not using contraception. The confusion comes from the fact that if pregnancy does occur with an IUD in place, it is more likely to be ectopic than a pregnancy without an IUD. But because IUDs prevent the vast majority of pregnancies in the first place, the absolute risk of ectopic pregnancy is very low.
Choosing Between Them
If pure pregnancy prevention is your only criterion, Liletta and Kyleena have the lowest first-year failure rates at 0.15 and 0.16 per 100 users. But the practical differences between any two IUDs are tiny, and other factors often matter more in real life.
The copper IUD is the clear choice if you want to avoid hormones entirely, need the longest possible duration without replacement, or need emergency contraception (it can be inserted up to 5 days after unprotected sex). Hormonal IUDs tend to reduce menstrual bleeding and cramping over time, with many users of the higher-dose devices experiencing very light periods or none at all. The copper IUD, by contrast, often makes periods heavier and crampier, particularly in the first several months.
Skyla and Kyleena are physically smaller than Mirena and Liletta, which can make insertion more comfortable for people with a smaller uterus or who have never been pregnant. Skyla’s slightly higher failure rate (0.41 per 100) and shorter 3-year lifespan are tradeoffs for that smaller size, though it still vastly outperforms the pill, patch, ring, or condoms.
The bottom line: all five IUDs available in the U.S. are over 99% effective. Hormonal IUDs have a measurable edge in failure rates, with Liletta and Kyleena at the top. But the copper IUD compensates with hormone-free protection, the longest approved duration, and unmatched effectiveness as emergency contraception. For most people, the best IUD is the one whose side effect profile and lifespan fit their life.