Mirena (Intra-uterine system)

What is it?

  • A small, flexible piece of soft plastic that fits inside the womb.
  • It is easily inserted by a trained health care professional.
  • It releases a hormone progesterone into the womb.

How does it work?

  • The hormone thickens the mucus at the entrance to the womb preventing sperm getting through and thins the lining of your womb preventing implantation of a fertilised egg. It may also stop ovulation (eggs being released from the ovaries) in some women.

What’s great about it?

  • Extremely effective (>99%). Less than 1 in 100 women using it will fall pregnant over 5 years.
  • Contraception lasts for 5 years unless you want it removed earlier.
  • Periods usually become lighter, shorter and sometimes less painful.
  • Can be used by women who have never had a baby.
  • Fertility returns as soon as it is removed.
  • There will be no need to take pills, interrupt sex or attend clinic regularly after insertion.
  • Is not affected by other medications.

What’s not so great about it?

  • No protection against sexually transmitted infections (STIs) - condoms advised.
  • Insertion can be slightly uncomfortable. Local anaesthetic is offered.
  • Can cause irregular periods or no periods.
  • Can become displaced or fall out (expulsion) but this is uncommon (5 in 100) and you can do checks yourself to make sure it’s in place.
  • Small risk of pelvic infection for up to 3 weeks after insertion. This risk is reduced by having a sexual health screen prior to the fitting.
  • Very small risk of perforating the womb or cervix (1 in 2000 risk).

Where can I get it?

  • Click here to text for an appointment at Chelsea and Westminster Sexual Health service. A preliminary appointment is usually required before fitting this method to discuss the method fully, screen for infections and schedule a fitting date.
  • Family planning clinics, some GPs and other sexual health clinics.

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