Hormonal IUD

The hormonal IUD is a small T-shaped device placed inside the uterus that releases the progestin levonorgestrel locally. Available brands in the US include Mirena (52mg, up to 8 years), Liletta (52mg, up to 8 years), Kyleena (19.5mg, up to 5 years), and Skyla (13.5mg, up to 3 years). Higher-dose devices last longer and have stronger systemic effects; lower-dose devices have lighter bleeding effects.

Efficacy is among the highest of any reversible contraceptive, above 99% in both typical and perfect use, because compliance is not user-dependent after insertion.

This is informational, not medical advice. IUD insertion and choice should be discussed with a qualified provider.

How it works

Three mechanisms stack:

  1. Cervical mucus thickening. The dominant local effect, blocking sperm.
  2. Endometrial thinning. The lining becomes thin and unsupportive of implantation, which is also why periods become lighter or stop.
  3. Partial ovulation suppression. Levonorgestrel reaches the bloodstream in small amounts. Suppression rates vary by dose: roughly 50% of cycles for Skyla and Kyleena (lower dose), and a higher proportion of early cycles for Mirena, declining over the 5-year mark.

Because suppression is partial and decreases over time, many hormonal-IUD users still ovulate, especially after the first 12 to 18 months.

Cycle implications

This is the most important nuance for cycle syncing. The hormonal IUD does not necessarily flatten the menstrual cycle the way the combined pill does. If you ovulate, you still have a follicular phase and luteal phase hormonally, even if bleeding is light or absent.

What this means in practice:

  • Bleeding pattern is a poor proxy for phase. Many users go months without bleeding while still cycling normally.
  • Direct ovulation tracking (BBT or OPK) is the only reliable way to confirm phase timing.
  • Cycle syncing can partially apply if you confirm ovulation. If you do not ovulate (more likely on Mirena early on or with hormonal sensitivity), the four-phase model does not.

Common side effects

  • Irregular bleeding in the first 3 to 6 months, often improving substantially.
  • Lighter or absent periods after the first year.
  • Cramping during and immediately after insertion (often significant; ask providers about pain management options).
  • Ovarian cysts (functional, usually resolving on their own).
  • Mood changes in a subset of users. Systemic effects are smaller than oral progestins but not zero.
  • Acne or oilier skin in some users.
  • Headaches.

Rare but serious risks: device expulsion (most common in the first 3 months, especially after recent childbirth), uterine perforation at insertion (rare), and pelvic infection in the first 20 days.

When to consider

  • Want long-acting reversible contraception without daily compliance.
  • Heavy bleeding (menorrhagia) is a problem; the hormonal IUD substantially reduces bleeding for most users.
  • Endometriosis or adenomyosis symptom management.
  • Estrogen is contraindicated.

When NOT to consider

  • Active pelvic infection or untreated cervical infection.
  • Distorted uterine cavity (severe fibroids, anatomic abnormalities) that prevents proper placement.
  • Unexplained uterine bleeding before workup.
  • History of certain pelvic cancers.

The copper IUD is a non-hormonal alternative for users who want a long-acting method without progestin.

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