It depends on the type. Hormonal IUDs release a small, steady dose of synthetic progesterone directly into the uterus, which does affect your hormones, though far less than birth control pills. The copper IUD contains no hormones at all and has no effect on your body’s hormone production.
Understanding the difference, and how much hormonal exposure each option actually involves, can help you decide which type fits your body and your priorities.
How Hormonal IUDs Work
All hormonal IUDs use the same active ingredient: levonorgestrel, a synthetic form of progesterone. The device sits inside your uterus and releases levonorgestrel locally, thinning the uterine lining and thickening cervical mucus so sperm can’t reach an egg. Four brands are currently available, and they differ mainly in how much hormone they contain and release each day:
- Mirena and Liletta contain 52 mg of levonorgestrel total. They release about 20 to 21 mcg per day initially, dropping to roughly 7 mcg per day by year eight.
- Kyleena contains 19.5 mg and starts at about 17.5 mcg per day, declining to 7.4 mcg per day after five years.
- Skyla contains the least at 13.5 mg, releasing about 14 mcg per day initially and dropping to 5 mcg per day after three years.
That steady decline matters. A Mirena releasing 19 mcg per day in its first year is putting out less than half that amount by year eight. Your hormonal exposure isn’t constant over the life of the device; it tapers significantly.
Much Less Hormonal Exposure Than the Pill
One of the biggest misconceptions is that a hormonal IUD floods your body with hormones the way oral contraceptives do. It doesn’t come close. A pharmacokinetic comparison published in the European Journal of Contraception and Reproductive Health Care found that combined oral contraceptives produce peak blood levels of levonorgestrel about 18 times higher than a hormonal IUD. On average, the pill results in roughly 9 times more levonorgestrel circulating in your bloodstream at steady state.
The reason is simple: the IUD delivers its hormone directly where it’s needed, inside the uterus. Only a small fraction absorbs into your general circulation. A birth control pill, by contrast, has to travel through your digestive system and bloodstream to reach reproductive tissues, so the dose has to be much larger. Even progestin-only pills (the “mini pill”) produce average blood levels about 1.7 times higher than the IUD.
Ovulation Usually Continues
Because systemic hormone levels stay so low, most hormonal IUD users keep ovulating normally. A study following long-term users found that 78.5% of menstrual cycles were ovulatory after six years of use. Only about 14% of cycles were anovulatory, and no participants experienced complete suppression of ovulation. This is a major distinction from the pill or hormonal implant, both of which work primarily by stopping ovulation altogether.
Your ovaries continue producing estrogen and progesterone on their natural cycle. The IUD’s contraceptive effect comes from local changes in the uterus and cervix, not from shutting down your ovarian hormones.
Hormonal Side Effects Are Still Possible
Lower systemic exposure doesn’t mean zero systemic exposure. Some levonorgestrel does enter your bloodstream, and some people are more sensitive to it than others. Clinical trials comparing hormonal IUDs to copper IUDs found that hormonal IUD users reported significantly more acne, mood changes, headaches, breast tenderness, and weight changes.
For mood specifically, depression and emotional disturbances are among the more commonly reported concerns. These effects don’t happen to everyone, but they’re real and well-documented in the medical literature. If you’ve had mood sensitivity to hormonal birth control in the past, it’s worth factoring in, even though the dose is lower than other methods.
Acne is another frequently mentioned side effect. Levonorgestrel has mild androgenic activity, meaning it can behave somewhat like a male hormone in the body. For some people this triggers breakouts, particularly if their skin was previously clear on a combined pill that actively suppresses androgens.
Period Changes and Amenorrhea
The most noticeable hormonal effect for most users is a change in menstrual bleeding. The local action of levonorgestrel thins the uterine lining, which typically makes periods lighter. About 18 to 19% of Mirena and Liletta users stop getting a period entirely by the end of the first year. This is a result of the thinned lining, not a sign that something is wrong with your hormones or fertility.
Irregular spotting is common in the first three to six months as your uterus adjusts. After that initial phase, most people settle into lighter, shorter periods or no periods at all. Skyla and Kyleena, which release less hormone, are less likely to cause complete amenorrhea but still tend to lighten bleeding.
Weight and Hormonal IUDs
A multicenter randomized trial tracked weight changes over three years in people using hormonal implants versus copper IUD users (who served as a non-hormonal comparison group). Copper IUD users gained an average of 1.1 kg over 36 months. Hormonal implant users, who have higher systemic progestin levels, gained about 3 kg. While this particular study used the copper IUD as a control rather than testing hormonal IUDs directly, it reinforces the pattern: lower systemic progestin exposure correlates with less weight change. The researchers concluded that even in the implant group, the weight gain had “little clinical significance.”
The Copper IUD Has No Hormonal Effect
The copper IUD (Paragard) works through an entirely different mechanism. Copper ions create an environment in the uterus that is toxic to sperm. It contains no synthetic hormones, releases no hormones, and does not interfere with your natural estrogen or progesterone production. Your menstrual cycle, ovulation, and hormonal fluctuations continue completely unchanged.
The tradeoff is that copper IUDs tend to make periods heavier and crampier, especially in the first several months. But for anyone who wants to avoid synthetic hormones entirely, whether due to past side effects, hormone-sensitive conditions, or personal preference, the copper IUD is the only long-acting option that leaves your endocrine system untouched.
Who Should Avoid Hormonal IUDs
Because hormonal IUDs do release a progestin, they’re not appropriate for everyone. Medical guidelines list current or past breast cancer as a contraindication for progestin-only contraceptives, including hormonal IUDs. Unexplained vaginal bleeding and suspected pregnancy are also reasons not to use one. For people with these conditions, the copper IUD remains an effective alternative that avoids hormonal exposure entirely.