Work by releasing progestin. Progestin is a hormone used in many kinds of birth control pills. It prevents the ovaries from releasing an egg.
Have a T-shape that also blocks the sperm and keeps sperm from reaching an egg.
Can stay in the uterus for 3 to 5 years. How long depends on the brand. There are 2 brands available in the United States: Skyla and Mirena. Mirena can also treat heavy menstrual bleeding and reduce cramps.
How IUDs work
Both types of IUDs prevent sperm from fertilizing an egg.
Progestin-releasing IUDs also works by:
Making the mucus around the cervix thicker, which makes it harder for sperm get inside the uterus and fertilize an egg
Thinning the lining of the uterus, which makes it more difficult for a fertilized egg to attach
Pros and cons
IUDs have certain benefits.
They are more than 99% effective at preventing pregnancy.
You don't need to think about birth control each time you have sex.
One IUD can last for 3 to 10 years. This makes it one of the cheapest forms of birth control.
You become fertile again almost immediately after an IUD is removed.
Copper-releasing IUDs do not have hormonal side effects and may help protect against uterine (endometrial) cancer.
Both types of IUDs may lower the risk of developing cervical cancer.
There are also downsides.
IUDs do not prevent sexually transmitted diseases (STDs). To avoid STDs you need to abstain from sex, be in a mutually monogamous relationship, or use condoms.
A health provider needs to insert or remove the IUD.
While rare, an IUD can slip out of place and need to be removed.
Copper-releasing IUDs can cause cramps, longer and heavier menstrual periods, and spotting between periods.
Progestin-releasing IUDs can cause irregular bleeding and spotting during the first few months.
IUDs may increase the risk for ectopic pregnancy. But women who use IUDs have a very low risk for getting pregnant.
Some types of IUDs may increase the risk for benign ovarian cysts. But such cysts usually do not cause symptoms and they usually resolve on their own.
IUDs do not appear to increase the risk for pelvic infection. They also do not affect fertility or increase the risk for infertility. Once an IUD is removed, fertility is restored.
Things to think about
You may want to consider an IUD if you:
Want or need to avoid risks of contraceptive hormones
Can't take hormonal contraceptives
Have a heavy menstrual flow and want lighter periods (hormonal IUD only)
You should not consider an IUD if you:
Are at high risk for STDs
Have a current or recent history of pelvic infection
Have abnormal Pap tests
Have cervical or uterine cancer
Have a very large or very small uterus
Bope ET, Kellerman RD. Women's Health. In: Bope ET, Kellerman RD, eds. Conn's Current Therapy 2017. Philadelphia, PA: Elsevier; 2016:chap 17.
Rivlin K, Westhoff C. Family planning. In: Lobo RA, Gershenson DM, Lentz GM, Valea FA, eds. Comprehensive Gynecology. 7th ed. Philadelphia, PA: Elsevier; 2017:chap 13.
Schreiber CA, Barnhart K. Contraception. In: Strauss JF, Barbieri RL, eds. Yen & Jaffe's Reproductive Endocrinology. 7th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 36.
Yoost J. Understanding benefits and addressing misperceptions and barriers to intrauterine devices access among populations in the United States. Patient Prefer Adherence. 2014;8:947-957. PMID: 25050062 www.ncbi.nlm.nih.gov/pubmed/25050062.
Irina Burd, MD, PhD, Associate Professor of Gynecology and Obstetrics at Johns Hopkins University School of Medicine, Baltimore, MD. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.