Intrauterine System (IUS) Mirena*
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• What is it?
• How does it work?
• How effective is it in preventing pregnancy?
• What are the advantages?
• What are the disadvantages?

What is it?
An IUS (Mirena*) is a small, plastic, T-shaped device that contains the hormone levonorgestrel. This device is placed inside a woman's uterus to prevent pregnancy. It can be left in place for up to 5 years.

How does it work?
The hormone in the IUS is released slowly over time and acts on the lining of the uterus, thereby preventing pregnancy in three ways:

• Thickens cervical mucous making it difficult for sperm to get through
• Causes changes in the lining of the uterus that helps to prevent implantation
• In some women, it prevents the ovaries from releasing an egg
• More detailed information on Mirena

How effective is it in preventing pregnancy?

• The IUS is more than 99% effective in preventing pregnancy.

What are the advantages?

• Very effective and long-acting (can be left in place up to 5 years)
• Does not contain estrogen
• Does not interfere with intercourse
• Decreases menstrual bleeding and cramping
• May reduce pain caused by endometriosis
• May lower the risk of precancerous cells developing in the uterus
• 20-30% of women will stop having periods
• Fast return of fertility once the IUS has been removed

What are the disadvantages?

• Must be inserted and removed by a trained health care professional
• Possible side effects include irregular bleeding or spotting in the first months after insertion
• Perforation of the uterus may occur at the time of insertion (rare)
• May fall out in up to 6% of women
• Does not protect against sexually transmitted infections