Intrauterine devices, better known as IUDs, are an extremely effective method of birth control. But which one is right for you? Currently, three FDA-approved brands of IUDs are available on the market: Paragard, Mirena, and Skyla.

If you’re considering which would be better for you, Dr. Alane Park, OB/GYN at Good Samaritan Hospital in Los Angeles, has some insight.

“My patients and I really like all three IUDs,” says Dr. Park, adding that while they don’t protect against sexually transmitted infections, “they are the most effective birth control method next to tubal ligation and vasectomy.”

Less than one in 100 women who use an IUD get pregnant each year. There is a slight chance you will have an ectopic pregnancy if you do get pregnant while using an IUD, but this risk is so low that it’s lower than the likelihood of an ectopic pregnancy without an IUD.

How Do IUDs Work?

An IUD has to be prescribed by a doctor, who will insert it into your uterus during a simple outpatient procedure. Paragard is partially made of copper, and it releases copper ions within the uterus. The copper produces an inflammatory reaction within the uterus and essentially creates a ‘toxic environment’ for sperm, thus prohibiting the sperm from fertilizing the woman’s eggs. Mirena and Skyla, meanwhile, contain hormones that affect ovulation. The hormones also thicken cervical mucus, making it difficult for sperm to pass into the uterus.

All three IUDs can stay implanted in your uterus for several years.

Comparing Devices



All IUDs are T-shaped, with a monofilament string attached to the bottom of the T. However, they do vary by size, as you can see in the above diagram.

“The older IUDs used braided string,” says Park. “The grooves in the braided strands passed bacteria into the uterus. Monofilament eliminates that risk.”

What They Contain

Mirena: Polyethylene T-shape holding a steroid reservoir containing 52 mg of the progestin hormone levonorgestrel. Approximately 20 mcg of hormone is released every day at the beginning of the device’s life, but this drops to about 10 mcg per day as it reaches expiration. 

Paragard: Polyethylene base, 176 mg of copper wire coiled around the vertical stem, and a 68.7 mg of copper wrapping on each side of the horizontal arm.

Skyla: Polyethylene T-shape holding a steroid reservoir with 13.5 mg of the progestin hormone levonorgestrel. Approximately 14 mcg of hormone is released per day for 25 days. After that, it releases 5 mcg every day for the next three years.

Side Effects

Mirena: Possible side effects include changes in your period, including having no period at all. You may develop acne, breast tenderness, ovarian cysts, or have a depressed mood. You might also have abdominal or pelvic pain. 

Paragard: You may have an allergic reaction to the copper, or experience increased menstrual bleeding and discomfort. You also might have backaches and cramps when you’re not having a period. Some women experience longer periods.

Skyla: As with Mirena, you might experience some changes in your period, including having no period at all. Some women experience increased menstrual bleeding and discomfort. You might also develop ovarian cysts, acne, or breast tenderness, or have abdominal or pelvic pain and a depressed mood.

Insertion and Removal

The best time to insert an IUD is in the middle of your period, when your cervix is more open. You might experience some cramping and a little bleeding. There is a very small risk of the IUD piercing your uterine wall on insertion, but this is rare. IUDs can be inserted after you deliver a baby or have had an abortion.


All IUDs are inserted at a doctor’s office or women’s health clinic. The doctor will give you a pelvic exam to make sure you don’t have any infections (if you do, they’ll need to be treated before the IUD can be inserted). The device will then be implanted using a very narrow tool that is inserted in the cervix. This tool keeps the horizontal arms of the T closed. The attachment string hangs through the neck of your cervix, where you’ll be able to feel it with your fingers.


All three devices have a small risk of being expelled from your uterus. Statistically, expulsion rates for IUDs are 4 percent or less. If your device comes out and you’re unaware of it, you could be at risk for pregnancy. That’s why it’s a good idea to check the location of the device’s string each month.


Removing an IUD is also something that needs to be done at a doctor’s office or clinic. The doctor will remove the device by gently pulling on the string. The horizontal T arms fold together and the device slides out.

The Takeaway

How do Dr. Park’s patients choose which device they want? “Some of my patients don’t want anything to do with hormones, so they choose Paragard,” she says. But she points out that the hormones in Mirena and Skyla are only released locally and don’t have the same kind of broad effect as the hormones in birth control pills.

“No one who has had cervical or uterine cancer should use either of the hormonal IUDs,” says Park. “On the other hand, if you already have heavy bleeding and cramping during your period, you probably don't want to use Paragard.”

Dr. Park always checks the device one month after insertion to make sure it’s in place and to check with the patient about side effects.