Less than 1 percent of women who use Mirena will get pregnant in the first year of typical use. If you do conceive while using Mirena, you're at higher risk of an ectopic pregnancy — when the fertilized egg implants outside the uterus, usually in a fallopian tube. However, because Mirena prevents most pregnancies, women who use it are at lower risk of having an ectopic pregnancy than are other sexually active women who are not using contraception.

Mirena doesn't offer protection from sexually transmitted infections (STIs).

Side effects associated with Mirena include:

  • Headache
  • Acne
  • Breast tenderness
  • Breakthrough bleeding
  • Absence of periods (amenorrhea), especially after one year of use
  • Mood changes
  • Weight gain
  • Ovarian cysts
  • Abdominal or pelvic pain

It's also possible to expel Mirena from your uterus. You may be more likely to expel Mirena if you:

  • Have never been pregnant
  • Have heavy or prolonged periods
  • Have severe menstrual pain
  • Previously expelled an IUD
  • Are younger than age 20
  • Had Mirena inserted immediately after childbirth or an abortion

In addition, your health care provider may recommend removal of Mirena if you develop:

  • A pelvic infection
  • Inflammation of the endometrium (endometritis)
  • Endometrial or cervical cancer
  • Uterine or cervical perforation
  • A significant increase in blood pressure
Jan. 21, 2012