ParaGard is a hormone-free intrauterine device (IUD) made with copper that prevents pregnancy for up to 10 years. Mirena is an IUD made of plastic that contains a reservoir of the hormone levonorgestrel and can prevent pregnancy for up to 8 years.

Which one is more effective at preventing pregnancy

Both ParaGard and Mirena are over 99% effective at preventing pregnancy (Mirena 99.8% effective, ParaGard 99.2-99.4% effective).

In the rare event that you become pregnant with an IUD in place, see your doctor straight away.

Are there differences in the way they work?

ParaGard contains copper, and a small amount is continuously released into the uterine cavity. Copper interferes with sperm motility and egg fertilization. If an egg does end up fertilized, ParaGard can also help prevent implantation into the endometrial lining.

The Mirena IUD continually releases a low dose of levonorgestrel (20 micrograms per day) which prevents the endometrial lining from thickening (which happens during a normal menstrual cycle, just before the lining is shed), thereby making the lining inhospitable to implantation by a fertilized egg. Levonorgestrel also causes cervical mucus to thicken and makes it harder for sperm to move.

Which one works faster?

IUDs are usually fitted during a period or within seven days of a period. This ensures a woman is not pregnant before the IUD is inserted. IUDs can be fitted at other times but a pregnancy test may be required beforehand.

ParaGard is effective immediately. It is also approved for use within 5 days of unplanned sexual intercourse as a form of emergency contraception.

Mirena is also effective immediately if fitted during the first seven days of menstruation, or if a reliable contraceptive method is being used; however, your doctor may recommend you do not have intercourse or use tampons for up to 24 hours after insertion to minimize the risk of infection.

Neither device protects against sexually transmitted infections (STIs) and all IUDs should only be inserted and removed by health care professionals experienced with the procedure.

How long do they last?

ParaGard will work for up to 10 years (although some research suggests it may last up to 20 years), and Mirena can be used for up to eight years. An IUD can be removed at any time, and fertility will return to what is normal for the woman once it is removed.

Which is less likely to cause bleeding?

Bleeding problems, including heavy bleeding, spotting between periods and cramping are common for the first 2-3 months after ParaGard insertion. On average, ParaGard increases the duration and amount of menstrual bleeding resulting in an approximately 50% greater blood loss. Women should talk to their doctor if these changes persist or they have any concerns. Ongoing bleeding problems are a common reason women request removal of ParaGard.

Levonorgestrel (contained in Mirena) can cause changes in a woman's bleeding patterns. Spotting may occur for the first few months and subsequent periods are likely to be lighter and shorter. 20% of women experience a complete cessation of periods within a year of starting Mirena. Mirena is also the only IUD approved to treat heavy periods, and it is very effective for this, with an 80% reduction in bleeding after three months and a 90% reduction in bleeding after 6 months. This is attributable to the continual release of low-dose levonorgestrel (20 micrograms per day) contained in Mirena that prevents the endometrial lining from thickening up, which is what happens during a normal menstrual cycle. Mirena represents a much more acceptable treatment for heavy menstrual bleeding than hysterectomy.

Any differences in suitability for different women?

Labeling for Mirena states that it is recommended for women who have had at least one child. Labelling for ParaGard was changed in 2005 to state that it is suitable for women in all stages of reproductive life from age 16 to menopause who are in a stable relationship and not at high risk of sexually transmitted infections (STIs) (so it can be used by women who have not had children).

ParaGard is a good contraceptive choice for women who cannot tolerate estrogen or desire a hormone-free contraceptive. The hormone contained in Mirena, levonorgestrel, is a progestogen so Mirena may also be used by women who are intolerant of, or prefer not to use, estrogen. Both ParaGard and Mirena may be used while breastfeeding.

Which has more side effects?

Longer periods and spotting between periods are the most common side effects of Paragard. Other side effects include abdominal pain, allergic reactions, anemia (low blood count), backache, cramps, painful sexual intercourse, vaginal infections or an unusual vaginal discharge. Theoretically, the copper in Paragard could exacerbate Wilson's Disease, a rare genetic condition affecting copper excretion.

In addition to bleeding changes, other side effects reported with Mirena include cramps, pelvic pain, abdominal pain, dizziness, headache or a migraine, ovarian cysts, acne, depressed or altered mood, nausea, breast tenderness, and fatigue.

All IUDs increase the risk of pelvic inflammatory disease, the risk is highest within 20 days of insertion. Rarely, IUDs may cause perforation of the uterus or embedment in the uterus requiring surgery. Expulsion of IUDs is more likely to occur during a woman's period, and if unnoticed, may result in a pregnancy.

Although IUDs lower the overall risk of having an ectopic pregnancy, if you do fall pregnant and have an IUD, the chance that it is an ectopic pregnancy is higher than normal. If you suspect you are pregnant and have an IUD in place always see your doctor straight away.

Size differences

ParaGard consists of a T-shaped frame measuring 32mm wide and 36mm high. The T-frame is made of polyethylene (plastic) and has approximately 176mg of copper coiled along the vertical stem and a 68.7mg copper collar on each side of the horizontal arm. Barium sulfate is mixed in with the polyethylene frame so it will show up in X-rays. ParaGard weighs less than 1gm and does not contain latex. ParaGard was first approved in 1984.

Mirena's frame is also T-shaped but is composed only of polyethylene mixed with barium to increase visibility on x-ray. Mirena is 32mm wide and high. There is a levonorgestrel-containing reservoir in the vertical stem that holds 52mg of levonorgestrel in total that is designed to release slowly over 5 years, delivering a daily dose of 20 micrograms of levonorgestrel. Mirena is latex-free and was first approved as a contraceptive in 2000 and for heavy menstrual bleeding in 2009.

Key points

Both ParaGard and Mirena are IUDs with over 99% effectiveness at preventing pregnancy. ParaGard contains copper and makes the uterine environment inhospitable to sperm and egg fertilization. Mirena contains levonorgestrel and increases the thickness of cervical mucus, slows sperm motility and reduces the thickness of the endometrial lining. Paragard is effective immediately after implantation and can also be used for emergency contraceptive purposes if inserted within five days of unprotected sexual intercourse. Mirena is effective immediately if inserted within seven days of the first day of a menstrual period and is also approved to treat heavy menstrual bleeding. ParaGard lasts at least ten years and Mirena lasts for eight. Paragard is more likely to cause heavier periods of longer duration whereas Mirena is more likely to cause amenorrhea (absence of periods).

See also: Drugs.com Compare Tool - Mirena vs ParaGard

Foot note

In 2013, Bayer released another levonorgestrel-containing IUD called Skyla, often called "Mirena's little sister". Skyla is slightly smaller than Mirena (28mm X 30mm) and contains a total of 13.5mg of levonorgestrel. It is designed to release 14 micrograms of levonorgestrel after 24 days of placement; this slowly declines over three years giving an average daily rate of 6 micrograms per day over three years. It also has a new inserter system that is different to Mirena, and the inserting tube is slightly narrower, which may make it easier and less painful to insert.

The smaller size of Skyla may be better tolerated by women with a smaller uterus, such as teens and perimenopausal women, and less likely to be expelled out of the uterus. The labeling of Skyla states that it can be used by women who have or have not had a child, whereas Mirena is recommended for women who have had at least one child, although experts consider it safe in women who have never had children. Skyla is approved in the USA only for contraception and is 99.1% effective. Skyla is less likely to cause periods to stop altogether (about 6% of women experience the complete cessation of periods with Skyla compared with 20% with Mirena).