A Mirena coil is a small T-shaped device that is fitted inside the uterus. It contains a hormone called levonorgestrel that is released in small amounts. The device is effective for up to 5 years, after which it should be removed and/or replaced.

Mirena coil is commonly used (but not limited to) for the following:

  • Contraception – >99% effective in preventing pregnancy
  • Treatment of heavy periods
  • Treatment of endometriosis
  • Treatment of endometrial hyperplasia (endometrial hyperplasia is a pre-cancer condition of overgrowth of the lining of the womb), thereby protecting the womb from developing cancer.
  • As part of HRT (hormone replacement therapy). If used as HRT, it should be replaced every 4 years.

If Mirena coil is fitted to help with heavy periods, it may take up to 3-4 months to see the beneficial effect. This is due to the small amounts of hormone it releases every day.

The side effects of Mirena coil are uncommon. These are period-like cramps, breast tenderness, acne and headaches, and tend to settle down on its own with continued use. Occasionally, it may fall out on its own.

Other rare complications include perforation of the womb, whereby the Mirena coil makes a small hole in the uterus. If this happens, you may need an operation to remove the coil.