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Middlesex-London Health Unit

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Intrauterine System (IUS)

The intrauterine system (IUS) is a small, T-shaped, soft plastic that contains small amounts of a hormone called levonorgestrel. It is called Mirena or Jaydess.


How does it work?

  • Releases the hormone slowly over time and acts on the lining of the uterus (womb).
  • Changes the lining and mucous of the cervix which makes it difficult for the sperm to get to a woman’s egg.


  • Mirena can stay in the uterus up to 5 years. Jaydess is effetive for up to 3 years.
  • No daily routine required.
  • Does not contain the hormone estrogen.
intra-uterine system
  • Okay for breastfeeding women to use.
  • Reduces menstrual cramps.
  • May reduce the risk of some forms of cancer (endometrial).
  • Some women may stop having menstrual periods.
  • Does not interfere with sex.


  • May cause irregular bleeding and spotting for the first 3-6 months.
  • A very small number of women will have the IUS come out on its own.
  • A monthly string check is recommended after menstrual period.

How to use an IUS

  • The IUS must be put in and taken out by a trained health care professional.

Typical success rate

99% effective.

Sexually transmitted infection (STI) protection

The IUS does not protect against STIs. Use a condom, dental dam, or glove every time you have sex. 1 2



Contact Us

For more information, please contact The Clinic at 519-663-5317.

Date of creation: July 26, 2011
Last modified on: May 20, 2022




1Bayer and Bayer Cross. (2012). Mirena. Retrieved from
2The Society of Obstetricians and Gynecologists. (2009). Choosing a contraceptive that is right for u. Retrieved from