Levonorgestrel-Releasing Intrauterine System

How Does It Work?

Levonorgestrel-releasing intrauterine system is a small device that is placed in the uterus by a healthcare provider. Once in place, it releases a low level of the progestin hormone levonorgestrel into the uterus. Levonorgestrel is thought to work in several ways to prevent pregnancy, including:
  • Thickening the cervical mucus, which makes it more difficult for sperm to enter the uterus
  • Inhibiting sperm movement
  • Reducing the ability of sperm to survive in the uterus
  • Thinning the lining of the uterus.
It is not entirely clear whether levonorgestrel-releasing intrauterine system affects ovulation. In clinical studies, 25 percent to 55 percent of women using Mirena did not ovulate. However, in clinical studies with Skyla, all but one woman studied continued to ovulate in the first and second year of use, and all the women studied ovulated in the third year of use.

Clinical Effects

Levonorgestrel-releasing intrauterine system is a very effective form of birth control. Fewer than 1 out of 100 women (1 percent) will become pregnant each year while using it. This is at least as effective as birth control pills, and much more effective than other types of birth control.

When and How to Use Levonorgestrel-Releasing Intrauterine System

Some general considerations to keep in mind while using this contraceptive include the following:
  • This medication is a small, plastic device that is placed into your uterus by a trained healthcare provider. It is usually inserted within seven days after your period starts, immediately after a first-trimester abortion or miscarriage, or at least six weeks after giving birth.  
  • The device is placed in the uterus using a slim, plastic inserter that comes with the medication. It only takes a few minutes for the device to be inserted.
  • You will need to return to your healthcare provider's office 4 to 12 weeks after insertion, and then at least once a year, to make sure the device is properly in place.
  • Some women experience some dizziness, pain, or bleeding during or right after placement. If your symptoms do not improve within 30 minutes, let your healthcare provider know. The device may not be placed properly.
  • Your healthcare provider may recommend a pain-reliever, such as acetaminophen (Tylenol®), before and/or after the device is placed. You can ask your healthcare provider about this.
  • You won't be able to feel levonorgestrel-releasing intrauterine system in your body, but will be able to feel the threads with your fingers at the top of your vagina (at your cervix). Do not pull on the threads, as doing so could displace the device.
  • You should check that the levonorgestrel-releasing intrauterine system is properly in place by feeling for the threads at least once a month after each menstrual period. If you do not feel the threads, or if you feel plastic, let your healthcare provider know right away. The device may not be properly placed and may not prevent pregnancy.
  • Although the product can remain in the uterus for three to five years, your healthcare provider can remove it at any time.
  • For the contraceptive to work properly, it must be used as prescribed. If levonorgestrel-releasing intrauterine system is not inserted properly, or if it becomes misplaced, it may not prevent pregnancy.
Last reviewed by: Kristi Monson, PharmD
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