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How Does the ParaGard IUD Work?

By Sarah Harding ; Updated June 13, 2017

The Device

ParaGard is one of only two intrauterine devices (IUD) used to prevent pregnancy. Unlike the other IUD, Mirena, ParaGard does not contain any synthetic hormones. The device itself is made of flexible plastic and copper molded into the shape of a small "T." Per, the "T" is slightly longer than one inch and has fine copper wire wrapped around the base and the arms. A small thread is located at the bottom of the device for removal.

Pregnancy Prevention

A woman must have ParaGard placed inside the uterus by a medical professional. Once the IUD is in place it can remain for up to 12 years per According to, only ideas about how the IUD works have been identified. ParaGard points out one notion is that sperm is destroyed. proposes this as well and suggests it may have something to do with the copper in the device. Planned Parenthood points out that the IUD affects the way sperm moves, which prevents them from fertilizing an egg. In the event that an egg is feritilized, ParaGard is said to prevent the embryo from implanting in the uterus, per Planned Parenthood points out that no evidence exists to support this theory, but the IUD does impact the lining of the uterus to prevent favorable conditions for pregnancy. maintains that the device does not impact the menstrual cycle in any way.


Even though a definitive description of how ParaGard works does not exist, the efficacy is clear. Planned Parenthood points out the failure rate of the IUD is less than one percent in ideal candidates. It can also be inserted within 120 hours of unprotected sex to prevent pregnancy at an efficacy rate of 99.9 percent, according to Planned Parenthood. Teens or women under 20 have a lowered efficacy rate, as do women whose IUD fell out of place. also points out that some women have discontinued the IUD due to bleeding and pain. Pregnancy after ParaGard use does occur, but in one study, 22 percent of women were not able to become pregnant one year after removing the device.

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