How Does ParaGard Work? The Science Behind a Copper IUD

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Fact-Checked by: Susana Restrepo, PhD

ParaGard is a contraceptive (birth control) known as an “intrauterine device” (IUD) that was first introduced in 1988. It is inserted into the uterus for pregnancy prevention and can also be used as a form of emergency contraception [1]. The effectiveness (success) of ParaGard in preventing pregnancy can last up to 10 years. This is based on clinical studies showing that less than 1% of women using ParaGard became pregnant [2]. Below is more information about the copper IUD and how it works.

Why Use ParaGard?

ParaGard is different from typical hormonal IUDs. Many women have certain medical restrictions (contraindications such as breast cancer) that prevent their use of common forms of hormonal birth control [3]. These women often turn to non-hormonal birth control methods such as ParaGard. Other women prefer ParaGard or other IUDs because [1]:

  • It can be removed at any time and conceiving may be attempted immediately after removal
  • It is safe to use while breastfeeding
  • It can be used for emergency contraception
  • It does not have the risks that some hormonal birth control methods possess, such as blood clots.

How Does ParaGard Work?

ParaGard is a non-hormonal IUD that contains copper as the pregnancy prevention agent [1]. For the moment, it is the only copper IUD available in the United States. ParaGard is a small and flexible “T-shaped” device that weighs less than 1 gram [2]. About 244.7 mg of copper wire wrap around the stem and arms of the plastic deceive to provide contraceptive effects. It is inserted by a medical provider into the uterus. Once in place, copper is continuously released into the uterus as copper ions (molecules with an electric charge).  

Understand the Science

Unlike some hormonal contraceptives, ParaGard (a non-hormonal contraceptive) does not stop ovulation (the process of ovaries producing eggs). So how does a copper IUD work to prevent pregnancy?

Copper is thought to interfere with processes required for pregnancy to occur once ovulation has happened. One of those processes is sperm transport.

Transport of sperm in the female reproductive tract involves them swimming through mucus in the cervix (passage from vaginal canal to uterus) and into the cervical canal [4]. When ParaGard is present, copper ions released into the mucus are thought to affect the sperm’s motility [5].

Another process that copper interferes with is fertilization of the egg (when the sperm successfully meets and penetrates the egg). Once in the uterus, the sperm make it into uterine tubes (fallopian tubes) which contain the ovulated eggs. When ParaGard is present, copper ions are thought to decrease sperm viability (ability to survive) [5]. As such, their ability to make it to the egg, and successfully penetrate the egg dramatically decreases. Eggs also lose some of their capacity to be fertilized after they are exposed to copper.

Copper is also thought to prevent implantation— a period about 14 days after sex in which a fertilized egg normally adheres to the uterine lining [2]. The copper does this by affecting the environment of the uterus to decrease egg receptivity.

For some time, it was thought that the contraceptive effect of ParaGard was due to the body’s inflammatory response to copper ions. However, a study found no inflammatory reaction in the endometrium (mucous membrane of the uterus) in women who had copper IUDs [6]. This means that inflammation may not explain the contraceptive effects of ParaGard.

ParaGard in Emergency Contraception

ParaGard also works as an emergency contraceptive [7]. It has been shown to be more effective than oral emergency contraceptive options. ParaGard must be inserted within 5 days of unprotected sex to be effective. Even if fertilization has occurred, ParaGard will prevent implantation of the fertilized egg.

Frequently Asked Questions:

What is ParaGard?

ParaGard is a copper IUD that is used to prevent pregnancy (as a contraceptive).

Can ParaGard be used as an emergency contraceptive?


How does the copper IUD work?

The copper on the IUD releases particles into the uterus that block the processes required for pregnancy to occur even after ovulation has happened.



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