Mirena is not a copper IUD. It is a hormonal IUD that releases a synthetic form of progesterone called levonorgestrel directly into the uterus. The only copper IUD available in the United States is ParaGard, which contains no hormones at all. Though both devices are T-shaped, sit inside the uterus, and prevent pregnancy with failure rates below 1%, they work in fundamentally different ways and have very different effects on your body.
How Mirena Works
Mirena continuously releases a small amount of levonorgestrel, a synthetic hormone, into the uterine cavity. This hormone works locally in a few ways: it thickens cervical mucus so sperm can’t pass through, it impairs sperm survival, and it thins the uterine lining. Because the hormone is released directly where it’s needed rather than circulating through your entire bloodstream, the dose is far lower than what you’d get from a birth control pill.
Mirena is FDA-approved for up to 8 years of pregnancy prevention. It also has a separate approval for treating heavy menstrual bleeding, though for that purpose it’s currently approved for up to 5 years at a time.
How the Copper IUD Works
ParaGard uses a completely different approach. Copper wire is wrapped around the plastic T-shaped frame, and that copper continuously releases ions into the uterus. These copper ions are toxic to sperm, interfering with their ability to move and fertilize an egg. No hormones are involved at any point. ParaGard is approved for up to 10 years of use, making it the longest-lasting reversible contraceptive available.
Because it’s hormone-free, ParaGard appeals to people who want to avoid hormonal side effects or who can’t use hormonal methods for medical reasons. It’s also used off-label as emergency contraception when inserted within five days of unprotected sex. A 2021 study funded by the National Institute of Child Health and Human Development found that the levonorgestrel IUD performed comparably to the copper IUD in this role, with a pregnancy rate of just 0.3% in the hormonal IUD group, but neither device has formal FDA approval for emergency contraception.
Effects on Your Period
This is where the two devices differ most dramatically, and it’s often the deciding factor for people choosing between them.
Mirena reduces menstrual bleeding by up to 90% within six months. About 20% of users stop getting a period entirely after one year, and that number climbs to 40% by year five. The first few months can involve unpredictable light spotting, but the overall trend is toward lighter or absent periods.
ParaGard does the opposite. Periods typically become heavier and longer, with roughly a 50% increase in blood loss. Cramping during periods can also intensify. These changes are most noticeable in the first three to six months and may improve somewhat over time, but ParaGard will never lighten your period. If you already deal with heavy or painful periods, this is an important consideration.
Other Hormonal IUD Options
Mirena isn’t the only hormonal IUD on the market. Several others release levonorgestrel at different doses, which affects how much they change your bleeding pattern and how long they last.
- Liletta is similar to Mirena in hormone dose. About 19% of users have no period at one year, rising to 38% by year three.
- Kyleena releases a lower dose. Around 12% of users lose their period at one year, and 23% by year five.
- Skyla has the lowest dose and shortest lifespan (3 years). Only about 6% of users stop menstruating at one year.
All four hormonal IUDs share a similar side effect profile: possible spotting in the first months, occasional ovarian cysts (usually harmless and temporary), headaches, and pelvic discomfort. The higher the hormone dose, the more likely you are to see a significant reduction in bleeding.
Choosing Between Hormonal and Copper
Both types are over 99% effective at preventing pregnancy, so efficacy alone won’t tip the scales. The real differences come down to hormones, periods, and duration.
A copper IUD makes sense if you want a completely hormone-free method, don’t mind heavier periods, or need the longest possible device lifespan without replacement. A hormonal IUD like Mirena makes sense if you want lighter periods (or none at all), need help managing heavy menstrual bleeding, or prefer a method that also treats certain uterine conditions.
Side effects also differ in character. With ParaGard, the main complaints are heavier bleeding and worse cramps. With Mirena and other hormonal IUDs, some people experience acne, headaches, or mood changes, though systemic hormonal effects tend to be milder than with oral contraceptives because the hormone acts mostly within the uterus. Neither type protects against sexually transmitted infections.