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Mirena® (52mg Intrauterine Delivery System Levonorgestrel)

Mechanism of Action

How does Mirena® work?​

How Mirena works

The contraceptive effect of Mirena® is based on a local effect of levonorgestrel

  1. The cervical mucus is thickened making it difficult for the sperm to get through to fertilise the egg.​

  2. Normal sperm movement and function inside the uterus and ovarian tubes is inhibited.​

  3. The growth of the lining of the uterus (endometrium) is reduced, which also makes menstrual blood loss much lighter and shorter.

Due to these changes in the endometrium, many women will have spotting and irregular bleeding during the first 3-6 months following the insertion of Mirena®. Thereafter, the strong suppression of the endometrium results in shorter and lighter periods.​

Understanding the bleeding pattern is an essential aspect of counselling and appropriate patient education has been shown to promote continuation

PP-MIR-IE-0070-1   |   January 2026

    • 1
      Mirena® Product monograph, 9th edition, 2010.
    • 2
      Peipert J, et al. Obstet Gynecol, 2011;117:1105–13​
    • 3
      Madden T, et al. Contraception, 2013;88(2):243–249.