Hormonal intrauterine device#Side effects

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| legal_AU_comment = {{cite web | title=Mirena (levonorgestrel) intrauterine device | website=Therapeutic Goods Administration (TGA) | date=17 July 2024 | url=https://www.tga.gov.au/resources/auspmd/mirena-levonorgestrel-intrauterine-device | access-date=12 October 2024}}

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| legal_US_comment = {{cite web | title=Kyleena- levonorgestrel intrauterine device | website=DailyMed | date=13 March 2023 | url=https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=2e07c155-21e1-4781-9633-ce8bddd47080 | access-date=19 April 2024 | archive-date=22 September 2023 | archive-url=https://web.archive.org/web/20230922030935/https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=2e07c155-21e1-4781-9633-ce8bddd47080 | url-status=live }}{{cite web | title=Skyla- levonorgestrel intrauterine device | website=DailyMed | date=31 January 2023 | url=https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9f44ff35-e052-49cd-a1c2-0bfd87d49309 | access-date=19 April 2024 | archive-date=9 December 2023 | archive-url=https://web.archive.org/web/20231209063424/https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9f44ff35-e052-49cd-a1c2-0bfd87d49309 | url-status=live }}{{cite web | title=Liletta- levonorgestrel intrauterine device | website=DailyMed | date=29 June 2023 | url=https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=aaf0eb2a-f88a-4f26-a445-0fd30176c326 | access-date=19 April 2024 | archive-date=29 November 2021 | archive-url=https://web.archive.org/web/20211129160734/https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=aaf0eb2a-f88a-4f26-a445-0fd30176c326 | url-status=live }}

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The hormonal IUD is an extremely effective method of birth control, and a 2021 study demonstrated that it may be used for emergency contraception.{{Cite web|date=4 February 2021|title=Science Update: Hormonal IUD as effective as a copper IUD at emergency contraception and with less discomfort, NICHD-funded study suggests|url=https://www.nichd.nih.gov/newsroom/news/020421-levonorgestrel|access-date=26 July 2021|archive-date=26 July 2021|archive-url=https://web.archive.org/web/20210726220347/https://www.nichd.nih.gov/newsroom/news/020421-levonorgestrel|url-status=live}} In addition to birth control, the hormonal IUD is used for prevention and treatment of:

• Heavy menstrual periods{{cite journal | vauthors = Bahamondes L, Bahamondes MV, Monteiro I | title = Levonorgestrel-releasing intrauterine system: uses and controversies | journal = Expert Review of Medical Devices | volume = 5 | issue = 4 | pages = 437–445 | date = July 2008 | pmid = 18573044 | doi = 10.1586/17434440.5.4.437 | s2cid = 659602 }}
• Endometriosis and chronic pelvic pain{{cite journal | vauthors = Petta CA, Ferriani RA, Abrao MS, Hassan D, Rosa E, Silva JC, Podgaec S, Bahamondes L | title = Randomized clinical trial of a levonorgestrel-releasing intrauterine system and a depot GnRH analogue for the treatment of chronic pelvic pain in women with endometriosis | journal = Human Reproduction | volume = 20 | issue = 7 | pages = 1993–1998 | date = July 2005 | pmid = 15790607 | doi = 10.1093/humrep/deh869 | doi-access = free }}
• Adenomyosis and dysmenorrhea{{cite journal | vauthors = Sheng J, Zhang WY, Zhang JP, Lu D | title = The LNG-IUS study on adenomyosis: a 3-year follow-up study on the efficacy and side effects of the use of levonorgestrel intrauterine system for the treatment of dysmenorrhea associated with adenomyosis | journal = Contraception | volume = 79 | issue = 3 | pages = 189–193 | date = March 2009 | pmid = 19185671 | doi = 10.1016/j.contraception.2008.11.004 }}
• Anemia{{cite journal | vauthors = Faundes A, Alvarez F, Brache V, Tejada AS | title = The role of the levonorgestrel intrauterine device in the prevention and treatment of iron deficiency anemia during fertility regulation | journal = International Journal of Gynaecology and Obstetrics | volume = 26 | issue = 3 | pages = 429–433 | date = June 1988 | pmid = 2900174 | doi = 10.1016/0020-7292(88)90341-4 | s2cid = 34592937 }}
• Endometrial hyperplasia (especially in pre-menopausal people who wish to maintain fertility in the treatment of endometrial hyperplasia){{cite journal | vauthors = | title = The American College of Obstetricians and Gynecologists Committee Opinion no. 631. Endometrial intraepithelial neoplasia | journal = Obstetrics and Gynecology | volume = 125 | issue = 5 | pages = 1272–1278 | date = May 2015 | pmid = 25932867 | doi = 10.1097/01.AOG.0000465189.50026.20 | s2cid = 46508283 }}{{cite journal | vauthors = Mittermeier T, Farrant C, Wise MR | title = Levonorgestrel-releasing intrauterine system for endometrial hyperplasia | journal = The Cochrane Database of Systematic Reviews | volume = 2020 | issue = 9 | pages = CD012658 | date = September 2020 | pmid = 32909630 | pmc = 8200645 | doi = 10.1002/14651858.CD012658.pub2 }}
• In some cases, use of a hormonal IUD may prevent a need for a hysterectomy.{{cite journal | vauthors = Marjoribanks J, Lethaby A, Farquhar C | title = Surgery versus medical therapy for heavy menstrual bleeding | journal = The Cochrane Database of Systematic Reviews | volume = 2016 | issue = 1 | pages = CD003855 | date = January 2016 | pmid = 26820670 | pmc = 7104515 | doi = 10.1002/14651858.CD003855.pub3 }}

Advantages:

• Considered one of the most effective forms of reversible birth control{{cite journal | vauthors = Winner B, Peipert JF, Zhao Q, Buckel C, Madden T, Allsworth JE, Secura GM | title = Effectiveness of long-acting reversible contraception | journal = The New England Journal of Medicine | volume = 366 | issue = 21 | pages = 1998–2007 | date = May 2012 | pmid = 22621627 | doi = 10.1056/NEJMoa1110855 | url = https://digitalcommons.wustl.edu/cgi/viewcontent.cgi?article=3776&context=open_access_pubs | access-date = 30 June 2019 | url-status = live | df = dmy-all | s2cid = 16812353 | doi-access = free | archive-url = https://web.archive.org/web/20200611191851/https://digitalcommons.wustl.edu/cgi/viewcontent.cgi?article=3776&context=open_access_pubs | archive-date = 11 June 2020 }}
• Can be used while breastfeeding (see also nursing mothers)
• No preparations needed before sex,{{cite web|title=IUD|url=http://www.plannedparenthood.org/learn/birth-control/iud|publisher=Planned Parenthood|access-date=18 June 2015|url-status=live|archive-url=https://web.archive.org/web/20150618161125/http://www.plannedparenthood.org/learn/birth-control/iud|archive-date=18 June 2015}} though routine checking of the device strings by patient and physician is advised to ensure proper placement remains intact{{cite web|title=Convenience|url=http://hcp.mirena-us.com/lets-talk-about-mirena/convenience.php | work = Let's Talk About Mirena |publisher=Bayer |access-date=18 June 2015|archive-url=https://web.archive.org/web/20150618115911/http://hcp.mirena-us.com/lets-talk-about-mirena/convenience.php|archive-date=18 June 2015}}
• 90% of users who wish to become pregnant do so within 24 months of removal.{{cite web|title=Mirena|url=http://www.rexall.ca/articles/view/1655/Mirena|publisher=MediResource Inc.|access-date=18 June 2015|url-status=live|archive-url=https://web.archive.org/web/20150703111314/http://www.rexall.ca/articles/view/1655/Mirena|archive-date=3 July 2015}}
• May experience lighter periods (some users stop having periods completely, see also amenorrhea){{cite journal | vauthors = Hidalgo M, Bahamondes L, Perrotti M, Diaz J, Dantas-Monteiro C, Petta C | title = Bleeding patterns and clinical performance of the levonorgestrel-releasing intrauterine system (Mirena) up to two years | journal = Contraception | volume = 65 | issue = 2 | pages = 129–132 | date = February 2002 | pmid = 11927115 | doi = 10.1016/s0010-7824(01)00302-x }}
• Effective for up to three to eight years (depending on the IUD)

Disadvantages:

• Irregular periods and spotting between periods often occurs after insertion This usually improves after three to six months.
• Moderate to severe discomfort may be experienced during insertion procedure, including uterine cramping and back pain.
• Other potential adverse effects and risks

After insertion, Mirena is effective at preventing pregnancy for up to eight years. Kyleena is approved for five years and Skyla is approved for three years.{{cite report| title= Highlights of Prescribing Information| url= https://www.accessdata.fda.gov/scripts/cder/daf/| date= 9 January 2013| url-status= live| archive-url= https://web.archive.org/web/20160506041852/http://www.accessdata.fda.gov/scripts/cder/drugsatfda/index.cfm?fuseaction=Search.Label_ApprovalHistory#apphist| archive-date= 6 May 2016| df= dmy-all}}{{Cite web|url=https://www.plannedparenthood.org/learn/birth-control/iud/hormonal-iuds|title=What are hormonal IUDs?|website=Planned Parenthood|access-date=19 April 2019|archive-date=24 April 2019|archive-url=https://web.archive.org/web/20190424145034/https://www.plannedparenthood.org/learn/birth-control/iud/hormonal-iuds|url-status=live}}

The hormonal IUD is a long-acting reversible contraceptive, and is considered one of the most effective forms of birth control. The first year failure rate for the hormonal IUD is 0.1-0.2% and the five-year failure rate is 0.7-0.9%.{{cite journal | vauthors = Westhoff CL, Keder LM, Gangestad A, Teal SB, Olariu AI, Creinin MD | title = Six-year contraceptive efficacy and continued safety of a levonorgestrel 52 mg intrauterine system | journal = Contraception | volume = 101 | issue = 3 | pages = 159–161 | date = March 2020 | pmid = 31786203 | doi = 10.1016/j.contraception.2019.10.010 | url = https://escholarship.org/uc/item/5kr8h999 | access-date = 2 January 2020 | url-status = live | s2cid = 208535090 | archive-url = https://web.archive.org/web/20200610162107/https://escholarship.org/uc/item/5kr8h999 | archive-date = 10 June 2020 }}{{Cite book|title=Speroff & Darney's clinical guide for contraception | veditors = Jensen JT, Creinin MD, Speroff L |year=2019|isbn=978-1-9751-0728-4|edition=Sixth|location=Philadelphia, PA |publisher=Wolters Kluwer |page=15|oclc=1121081247}} These rates are comparable to tubal sterilization, but unlike sterilization the effects of the hormonal IUD are reversible.

The hormonal IUD is considered to be more effective than other common forms of reversible contraception, such as the birth control pill, because it requires little action by the user after insertion. The effectiveness of other forms of birth control is mitigated (decreased) by the users themselves. If medication regimens for contraception are not followed precisely, the method becomes less effective. IUDs require no daily, weekly, or monthly regimen, so their typical use failure rate is therefore the same as their perfect use failure rate.

In a 10-year study, the levonorgestrel IUD was found to be as effective as oral medicines (tranexamic acid, mefenamic acid, combined oestrogen–progestogen or progesterone alone) for heavy periods; the same proportion of study participants had not had surgery for heavy bleeding and had similar improvements in their quality of life.{{cite journal | vauthors = Kai J, Dutton B, Vinogradova Y, Hilken N, Gupta J, Daniels J | title = Rates of medical or surgical treatment for women with heavy menstrual bleeding: the ECLIPSE trial 10-year observational follow-up study | language = EN | journal = Health Technology Assessment | volume = 27 | issue = 17 | pages = 1–50 | date = October 2023 | pmid = 37924269 | pmc = 10641716 | doi = 10.3310/JHSW0174 | url = https://www.journalslibrary.nihr.ac.uk/hta/jhsw0174/ | access-date = 12 April 2024 | url-status = live | archive-url = https://web.archive.org/web/20231106011541/https://www.journalslibrary.nihr.ac.uk/hta/JHSW0174 | archive-date = 6 November 2023 }}{{Cite journal |date=8 March 2024 |title=The coil and medicines are both effective long-term treatments for heavy periods |url=https://evidence.nihr.ac.uk/alert/the-coil-and-medicines-are-both-effective-long-term-treatments-for-heavy-periods/ |journal=NIHR Evidence |doi=10.3310/nihrevidence_62335 |access-date=12 April 2024 |archive-date=18 March 2024 |archive-url=https://web.archive.org/web/20240318004632/https://evidence.nihr.ac.uk/alert/the-coil-and-medicines-are-both-effective-long-term-treatments-for-heavy-periods/ |url-status=live |url-access=subscription |doi-access=free }}

In people with complete bicornuate uterus and in need of contraception, two IUDs are generally applied (one in each horn) due to lack of evidence of efficacy with only one IUD.{{cite journal| vauthors = Oelschlager AM, Debiec K, Micks E, Prager S |title=Use of the Levonorgestrel Intrauterine System in Adolescents With Known Uterine Didelphys or Unicornuate Uterus|journal=Journal of Pediatric and Adolescent Gynecology|volume=26|issue=2|year=2013|pages=e58|issn=1083-3188|doi=10.1016/j.jpag.2013.01.029|doi-access=free}} Evidence is lacking regarding progestogen IUD usage for menorrhagia in bicornuate uterus, but a case report showed good effect with a single IUD for this purpose.{{cite journal | vauthors = Acharya GP, Mills AM | title = Successful management of intractable menorrhagia with a levonorgestrel-releasing intrauterine device, in a woman with a bicornuate uterus | journal = Journal of Obstetrics and Gynaecology | volume = 18 | issue = 4 | pages = 392–393 | date = July 1998 | pmid = 15512123 | doi = 10.1080/01443619867263 }}

Progestogen-only contraceptives such as an IUD are not believed to affect milk supply or infant growth.{{cite journal | vauthors = Truitt ST, Fraser AB, Grimes DA, Gallo MF, Schulz KF | title = Combined hormonal versus nonhormonal versus progestin-only contraception in lactation | journal = The Cochrane Database of Systematic Reviews | issue = 2 | pages = CD003988 | year = 2003 | pmid = 12804497 | doi = 10.1002/14651858.CD003988 | veditors = Lopez LM }} However, a study in the Mirena application for FDA approval found a lower continuation of breastfeeding at 75 days in hormonal IUD users (44%) versus copper IUD users (79%).{{cite web | work = Center for Drug Evaluation and Research | publisher = U.S. Food and Drug Administration | title=Medical review of NDA 21-225: Mirena (levonorgestrel-releasing intrauterine system) Berlex Laboratories | date = December 2000 | url=http://www.fda.gov/cder/foi/nda/2000/21-225.pdf_Mirena_Medr.pdf | archive-url = https://web.archive.org/web/20080227041634/http://www.fda.gov/cder/foi/nda/2000/21-225.pdf_Mirena_Medr.pdf | archive-date = 27 February 2008 }}{{rp|37}}

When using Mirena, about 0.1% of the maternal dose of levonorgestrel can be transferred via milk to the

nursed infant.{{cite web | title = MIRENA Data Sheet | work = Bayer NZ | date = 11 December 2009 | url = http://www.bayerresources.com.au/resources/uploads/DataSheet/file9503.pdf | archive-url = https://web.archive.org/web/20110706101854/http://www.bayerresources.com.au/resources/uploads/DataSheet/file9503.pdf | archive-date = 6 July 2011 | access-date = 10 February 2011 }}

A six-year study of breastfed infants whose mothers used a levonorgestrel-only method of birth control found the infants had increased risk of respiratory infections and eye infections, though a lower risk of neurological conditions, compared to infants whose mothers used a copper IUD.{{cite journal | vauthors = Schiappacasse V, Díaz S, Zepeda A, Alvarado R, Herreros C | title = Health and growth of infants breastfed by Norplant contraceptive implants users: a six-year follow-up study | journal = Contraception | volume = 66 | issue = 1 | pages = 57–65 | date = July 2002 | pmid = 12169382 | doi = 10.1016/S0010-7824(02)00319-0 }} No longer-term studies have been performed to assess the long-term effects on infants of levonorgestrel in breast milk.

There are conflicting recommendations about use of Mirena while breastfeeding. The U.S. CDC does not recommend any hormonal method as a first choice of contraceptive for nursing mothers, although progestin-only methods, such as Mirena, may be used with close follow-up or when the benefits outweigh the risks.{{Cite web|date=9 April 2020|title=Classifications for Intrauterine Devices {{!}} CDC|url=https://www.cdc.gov/reproductivehealth/contraception/mmwr/mec/appendixb.html|access-date=7 July 2020|website=www.cdc.gov|language=en-us|archive-date=15 July 2020|archive-url=https://web.archive.org/web/20200715044125/https://www.cdc.gov/reproductivehealth/contraception/mmwr/mec/appendixb.html|url-status=live}} The World Health Organization recommends against immediate postpartum insertion, citing increased expulsion rates. It also reports concerns about potential effects on the infant's liver and brain development in the first six weeks postpartum. However, it recommends offering Mirena as a contraceptive option beginning at six weeks postpartum even to nursing women.{{cite book |vauthors=((World Health Organization)) |year=2015 |title=Medical eligibility criteria for contraceptive use |edition=5th |location=Geneva |publisher=World Health Organization |isbn=978-92-4-154915-8 |author-link=World Health Organization | hdl=10665/181468 | hdl-access=free}}{{cite web | author=World Health Organization | title=Medical eligibility criteria for contraceptive use, fifth edition 2015: executive summary | publisher=World Health Organization | date=2015 | url=https://apps.who.int/iris/handle/10665/172915 | hdl=10665/172915 | hdl-access=free | access-date=3 February 2020 | archive-date=28 August 2021 | archive-url=https://web.archive.org/web/20210828050018/https://apps.who.int/iris/handle/10665/172915 | url-status=live }} Planned Parenthood offers Mirena as a contraceptive option for those who are breastfeeding beginning at four weeks postpartum.{{cite web|date=July 2005|title=Understanding IUDs|url=http://www.plannedparenthood.org/birth-control-pregnancy/birth-control/intrauterine-devices.htm|archive-url=https://web.archive.org/web/20061012053613/http://www.plannedparenthood.org/birth-control-pregnancy/birth-control/intrauterine-devices.htm|archive-date=12 October 2006|access-date=8 October 2006|publisher=Planned Parenthood}}

A hormonal IUD should not be used by people who:

• Are, or think they may be, pregnant
• Have abnormal vaginal bleeding that has not been explained (controversial){{cite book |title=Heavy menstrual bleeding (update) |publisher=National Institute for Health and Care Excellence | date = 2018}}
• Have untreated cervical or uterine cancer
• Have, or may have, breast cancer
• Have abnormalities of the cervix or uterus (controversial)
• Have had pelvic inflammatory disease within the past three months
• Have had an STI such as chlamydia or gonorrhea within the past three months
• Have liver disease or tumor
• Have an allergy to levonorgestrel or any of the inactive ingredients included in the device

Insertion of an IUD is acceptable after a dilation and evacuation (D&E) abortion (second-trimester abortion), but may be associated with a higher expulsion rate.{{cite journal | vauthors = Roe AH, Bartz D | title = Society of Family Planning clinical recommendations: contraception after surgical abortion | journal = Contraception | volume = 99 | issue = 1 | pages = 2–9 | date = January 2019 | pmid = 30195718 | doi = 10.1016/j.contraception.2018.08.016 | doi-access = free }} To reduce the risk of infection, insertion of an IUD is not recommended for women that have had a medical abortion but have not yet had an ultrasound to confirm that the abortion was complete, or that have not yet had their first menstruation following the medical abortion.

A full list of contraindications can be found in the WHO Medical Eligibility Criteria for Contraceptive Use and the CDC United States Medical Eligibility Criteria for Contraceptive Use.{{cite book |author=WHO |year=2010 |chapter=Intrauterine devices (IUDs) |title=Medical Eligibility Criteria for Contraceptive Use |edition=4th |location=Geneva |publisher=Reproductive Health and Research, WHO |isbn=978-92-4-156388-8 |chapter-url=https://www.who.int/reproductivehealth/publications/family_planning/9789241563888/en/ |author-link=World Health Organization |archive-url=https://web.archive.org/web/20120710225029/http://www.who.int/reproductivehealth/publications/family_planning/9789241563888/en/ |archive-date=10 July 2012 }}

{{Further information|Progestogen (medication)#Side effects}}

• Irregular menstrual pattern: irregular bleeding and spotting is common in the first three to six months of use. After that time periods become shorter and lighter, and 20% of women stop having periods after one year of use.{{cite journal | vauthors = Hidalgo M, Bahamondes L, Perrotti M, Diaz J, Dantas-Monteiro C, Petta C | title = Bleeding patterns and clinical performance of the levonorgestrel-releasing intrauterine system (Mirena) up to two years | journal = Contraception | volume = 65 | issue = 2 | pages = 129–132 | date = February 2002 | pmid = 11927115 | doi = 10.1016/S0010-7824(01)00302-X }} The average user reports 16 days of bleeding or spotting in the first month of use, but this diminishes to about four days at 12 months.{{cite journal | vauthors = McCarthy L | date = May 2006 |title=Levonorgestrel-Releasing Intrauterine System (Mirena) for Contraception |journal=Am Fam Physician |volume=73 |issue=10 |pages=1799– |url=http://www.aafp.org/afp/20060515/steps.html |access-date=4 May 2007 |url-status=live |archive-url=https://web.archive.org/web/20070926230715/http://www.aafp.org/afp/20060515/steps.html |archive-date=26 September 2007 }}{{cite journal | vauthors = Rönnerdag M, Odlind V | title = Health effects of long-term use of the intrauterine levonorgestrel-releasing system. A follow-up study over 12 years of continuous use | journal = Acta Obstetricia et Gynecologica Scandinavica | volume = 78 | issue = 8 | pages = 716–721 | date = September 1999 | pmid = 10468065 | doi = 10.1034/j.1600-0412.1999.780810.x | doi-access = free }}
• Cramping and pain: many women feel discomfort or pain during and immediately after insertion. Some women may have cramping for the first 1–2 weeks after insertion.
• Expulsion: Sometimes the IUD can slip out of the uterus. This is termed expulsion. Around 5% of IUD users experience expulsion. If this happens a woman is not protected from pregnancy.{{cite journal | date = December 1995 | title = IUDs—An Update | journal = Population Reports | publisher = Population Information Program, Johns Hopkins School of Public Health | volume = XXII | issue = 5 }} Expulsion is more common in younger women, women who have not had children, and when an IUD is inserted immediately after childbirth or abortion.{{cite journal | date = December 1995 | title = IUDs—An Update: Chapter 2.7: Expulsion | journal = Population Reports | publisher = Population Information Program, Johns Hopkins School of Public Health | volume = XXII | issue = 5 | url=http://www.infoforhealth.org/pr/b6/b6chap2_7.shtml#top| url-status=dead| archive-url=https://web.archive.org/web/20060905183651/http://www.infoforhealth.org/pr/b6/B6chap2_7.shtml#top| archive-date=5 September 2006}}{{cite journal | date = December 1995 | title = IUDs—An Update: Chapter 3.3: Postpartum Insertion | journal = Population Reports | publisher = Population Information Program, Johns Hopkins School of Public Health | volume = XXII | issue = 5 | url= http://www.infoforhealth.org/pr/b6/b6chap3_3.shtml#top | url-status= dead | archive-url= https://web.archive.org/web/20060429204536/http://www.infoforhealth.org/pr/b6/b6chap3_3.shtml#top | archive-date= 29 April 2006 }}{{cite journal | date = December 1995 | title = IUDs—An Update: Chapter 3.4: Postabortion Insertion | journal = Population Reports | publisher = Population Information Program, Johns Hopkins School of Public Health | volume = XXII | issue = 5 | url= http://www.infoforhealth.org/pr/b6/b6chap3_4.shtml#top | url-status= dead | archive-url= https://web.archive.org/web/20060811161956/http://www.infoforhealth.org/pr/b6/b6chap3_4.shtml#top | archive-date= 11 August 2006 }}

• Perforation: Very rarely, the IUD can be pushed through the wall of the uterus during insertion. Risk of perforation is mostly determined by the skill of the practitioner performing the insertion. For experienced medical practitioners, the risk of perforation is one per 1,000 insertions or less.{{cite book | vauthors = ((WHO Scientific Group on the Mechanism of Action Safety and Efficacy of Intrauterine Devices)), ((World Health Organization)) | year = 1987 | title = Mechanism of action, safety and efficacy of intrauterine devices | location = Geneva | publisher = World Health Organization | hdl = 10665/38182 | hdl-access = free | id = World Health Organization technical report series; no. 753 | isbn = 92-4-120753-1 }} With postpartum insertions, perforation of the uterus is more likely to occur when uterine involution is incomplete; involution usually completes by 4–6 weeks postpartum. Special considerations apply to women who plan to breastfeed. If perforation does occur it can damage the internal organs, and in some cases surgery is needed to remove the IUD.
• Pregnancy complications: Although the risk of pregnancy with an IUD is very small, if one does occur there is an increased risk of serious problems. These include ectopic pregnancy, infection, miscarriage, and early labor and delivery. As many as half the pregnancies that occur in Mirena users may be ectopic. The incidence rate of ectopic pregnancies is approximately one per 1000 users per year.{{rp|3–4}} Immediate removal of the IUD is recommended in the case of pregnancy. No pattern of birth defects was found in the 35 babies for whom birth outcomes were available at the time of FDA approval.{{rp|5,41}}
• Infection: The insertion of the IUD does have a small risk of pelvic inflammatory disease (PID). Concurrent infection with gonorrhea or chlamydia at the time of insertion increases the risk of pelvic inflammatory disease.{{cite journal | vauthors = Grimes DA | title = Intrauterine device and upper-genital-tract infection | journal = Lancet | volume = 356 | issue = 9234 | pages = 1013–1019 | date = September 2000 | pmid = 11041414 | doi = 10.1016/S0140-6736(00)02699-4 | s2cid = 7760222 }} If PID does occur, it will most likely happen within 21 days of insertion. The device itself does not increase the risk of infection.
• Ovarian cysts: Enlarged follicles (ovarian cysts) have been diagnosed in about 12% of the subjects using a hormonal IUD in studies that use ultrasound to look for cysts, even if asymptomatic. In studies that only evaluate symptomatic cysts, only 4.5% of women complain of any ovarian cysts over 5 or more years of use, and only 0.3% require IUD removal for ovarian cysts.{{cite journal | vauthors = Teal SB, Turok DK, Chen BA, Kimble T, Olariu AI, Creinin MD | title = Five-Year Contraceptive Efficacy and Safety of a Levonorgestrel 52-mg Intrauterine System | journal = Obstetrics and Gynecology | volume = 133 | issue = 1 | pages = 63–70 | date = January 2019 | pmid = 30531565 | pmc = 6319579 | doi = 10.1097/AOG.0000000000003034 }} Thus, any issues with ovarian cysts are not of a clinically relevant nature. Most of these follicles are asymptomatic, although some may be accompanied by pelvic pain or dyspareunia. In most cases the enlarged follicles disappear spontaneously after two to three months. Surgical intervention is not usually required.{{cite journal | vauthors = Bahamondes L, Hidalgo M, Petta CA, Diaz J, Espejo-Arce X, Monteiro-Dantas C | title = Enlarged ovarian follicles in users of a levonorgestrel-releasing intrauterine system and contraceptive implant | journal = The Journal of Reproductive Medicine | volume = 48 | issue = 8 | pages = 637–640 | date = August 2003 | pmid = 12971147 }}
• Mental health changes including: nervousness, depressed mood, mood swings{{cite web|title=Mirena: Consumer Medicine Information|url=http://www.bayerresources.com.au/resources/uploads/CMI/file9398.pdf|publisher=Bayer|access-date=27 April 2014|date=March 2014|url-status=live|archive-url=https://web.archive.org/web/20140427203913/http://www.bayerresources.com.au/resources/uploads/CMI/file9398.pdf|archive-date=27 April 2014}}{{Further information|Progestogen (medication)#Mood changes}}
• Weight gain
• Headache, migraine
• Nausea
• Acne
• Excessive hairiness
• Lower abdominal or back pain
• Decreased libido
• Itching, redness or swelling of the vagina
• Vaginal discharge{{cite web|title=Mirena|url=http://www.medicines.org.uk/emc/medicine/1829/SPC/Mirena#UNDESIRABLE_EFFECTS|publisher=Bayer UK|access-date=18 June 2015|date=11 June 2013|url-status=live|archive-url=https://web.archive.org/web/20150618065037/http://www.medicines.org.uk/emc/medicine/1829/SPC/Mirena#UNDESIRABLE_EFFECTS|archive-date=18 June 2015}}
• Breast pain, tenderness
• Edema
• Abdominal distension
• Cervicitis
• Bacterial vaginosis{{cite journal | vauthors = Donders GG, Bellen G, Ruban K, Van Bulck B | title = Short- and long-term influence of the levonorgestrel-releasing intrauterine system (Mirena®) on vaginal microbiota and Candida | journal = Journal of Medical Microbiology | volume = 67 | issue = 3 | pages = 308–313 | date = March 2018 | pmid = 29458551 | doi = 10.1099/jmm.0.000657 | doi-access = free }}
• May affect glucose tolerance
• May experience a change in vision or contact lens tolerance
• May deplete vitamin B1 which can affect energy, mood, and nervous system functioning
• A "lost coil" occurs when the thread cannot be felt by a woman on routine checking and is not seen on speculum examination.{{cite journal | vauthors = Nijhuis JG, Schijf CP, Eskes TK | title = [The lost IUD: don't look too far for it] | journal = Nederlands Tijdschrift voor Geneeskunde | volume = 129 | issue = 30 | pages = 1409–1410 | date = July 1985 | pmid = 3900746 }} Various thread collector devices or simple forceps may then be used to try to grasp the device through the cervix.{{cite journal | vauthors = Kaplan NR | title = Letter: Lost IUD | journal = Obstetrics and Gynecology | volume = 47 | issue = 4 | pages = 508–509 | date = April 1976 | pmid = 1256735 }} In the rare cases when this is unsuccessful, an ultrasound scan may be arranged to check the position of the coil and exclude its perforation through into the abdominal cavity or its unrecognised previous expulsion.

According to a 1999 evaluation of the studies performed on progestin-only birth control by the International Agency for Research on Cancer, there is some evidence that progestin-only birth control reduces the risk of endometrial cancer. The IARC in 1999 concluded that there is no evidence progestin-only birth control increases the risk of any cancer, though the available studies were too small to be definitively conclusive.{{cite web |title=Hormonal Contraceptives, Progestogens Only |website=International Programme on Chemical Safety |year=1999 |url=http://www.inchem.org/documents/iarc/vol72/vol72-2.html |access-date=8 October 2006 |archive-url=https://web.archive.org/web/20060928033515/http://www.inchem.org/documents/iarc/vol72/vol72-2.html |archive-date=28 September 2006 }}

Progesterone is a hormone in the endometrium that counteracts estrogen driven growth.{{cite journal | vauthors = Kim JJ, Chapman-Davis E | title = Role of progesterone in endometrial cancer | journal = Seminars in Reproductive Medicine | volume = 28 | issue = 1 | pages = 81–90 | date = January 2010 | pmid = 20104432 | pmc = 4767501 | doi = 10.1055/s-0029-1242998 }} Very low levels of progesterone will cause estrogen to act more, leading to endometrial hyperplasia and adenocarcinoma. These effects can be minimized if treated with progestin, but not in very many cases.

Estrogen and progesterone have an antagonistic relationship. Estrogen promotes the growing of endometrial lining, while progesterone limits it. In the case of endometrial cancer, progesterone can negatively regulate estrogen driven growth. Tumors formed are correlated with insufficient progesterone and excess estrogen. In patients with endometrial cancer who use progestin releasing IUDs concluded mixed results.

A 2020 meta-analysis by Livia Conz et al. estimated that users of levonorgestrel-releasing systems had an increased breast cancer risk in general (with an odds ratio of 1.16) and higher risk for those over age 50 (odds ratio 1.52), and suggested balancing this risk against the known benefits of long-term use.{{cite journal | vauthors = Conz L, Mota BS, Bahamondes L, Teixeira Dória M, Françoise Mauricette Derchain S, Rieira R, Sarian LO | title = Levonorgestrel-releasing intrauterine system and breast cancer risk: A systematic review and meta-analysis | journal = Acta Obstetricia et Gynecologica Scandinavica | volume = 99 | issue = 8 | pages = 970–982 | date = August 2020 | pmid = 31990981 | doi = 10.1111/aogs.13817 | publisher = Wiley | s2cid = 210946832 | doi-access = free }} Researchers cautioned against causal interpretation from this study, citing confounding effects, methodological concerns and a 2020 meta-analysis of randomized controlled trials which showed no increased risk.{{cite journal | vauthors = Al Kiyumi MH, Al Battashi K, Al-Riyami HA | title = Levonorgestrel-releasing intrauterine system and breast cancer; Is there an association? | journal = Acta Obstetricia et Gynecologica Scandinavica | volume = 100 | issue = 9 | pages = 1749 | date = September 2021 | pmid = 34021506 | doi = 10.1111/aogs.14188 | publisher = Wiley | s2cid = 235094824 | doi-access = free }}{{cite journal | vauthors = Silva FR, Grande AJ, Da Rosa MI | title = Is the levonorgestrel-releasing intrauterine system a risk factor for breast cancer? | journal = Acta Obstetricia et Gynecologica Scandinavica | volume = 100 | issue = 2 | pages = 363–364 | date = February 2021 | pmid = 32740910 | doi = 10.1111/aogs.13966 | publisher = Wiley | s2cid = 220942002 | doi-access = free }}{{cite journal | vauthors = Romero SA, Young K, Hickey M, Su HI | title = Levonorgestrel intrauterine system for endometrial protection in women with breast cancer on adjuvant tamoxifen | journal = The Cochrane Database of Systematic Reviews | volume = 12 | issue = 12 | pages = CD007245 | date = December 2020 | pmid = 33348436 | pmc = 8092675 | doi = 10.1002/14651858.CD007245.pub4 | doi-access = free }}

No evidence has been identified to suggest Mirena affects bone mineral density (BMD).{{cite journal | vauthors = ((Faculty of Family Planning and Reproductive Health Care Clinical Effectiveness Unit)) | title = FFPRHC Guidance (April 2004). The levonorgestrel-releasing intrauterine system (LNG-IUS) in contraception and reproductive health | journal = The Journal of Family Planning and Reproductive Health Care | volume = 30 | issue = 2 | pages = 99–108; quiz 109 | date = April 2004 | pmid = 15086994 | doi = 10.1783/147118904322995474 | s2cid = 31281104 | doi-access = free }} Two small studies, limited to studying BMD in the forearm, show no decrease in BMD.{{cite journal | vauthors = Wong AY, Tang LC, Chin RK | title = Levonorgestrel-releasing intrauterine system (Mirena) and Depot medroxyprogesterone acetate (Depoprovera) as long-term maintenance therapy for patients with moderate and severe endometriosis: a randomised controlled trial | journal = The Australian & New Zealand Journal of Obstetrics & Gynaecology | volume = 50 | issue = 3 | pages = 273–279 | date = June 2010 | pmid = 20618247 | doi = 10.1111/j.1479-828X.2010.01152.x | s2cid = 22050651 }}{{cite journal | vauthors = Bahamondes MV, Monteiro I, Castro S, Espejo-Arce X, Bahamondes L | title = Prospective study of the forearm bone mineral density of long-term users of the levonorgestrel-releasing intrauterine system | journal = Human Reproduction | volume = 25 | issue = 5 | pages = 1158–1164 | date = May 2010 | pmid = 20185512 | doi = 10.1093/humrep/deq043 | doi-access = free }} One of the studies showed at seven years of use, similar BMD at the midshaft of the ulna and at the distal radius as nonusers matched by age and BMI. In addition, BMD measurements were similar to the expected values for women in the same age group as the participants. The authors of the study said their results were predictable, since it is well established that the main factor responsible for bone loss in women is hypoestrogenism, and, in agreement with previous reports, they found estradiol levels in Mirena users to be normal.

File:Mirena IUD - Roe Becken ap.jpg

The hormonal IUD is a small T-shaped piece of plastic, which contains levonorgestrel, a type of progestin.{{cite web |url=http://www.mirena-us.com/ |title=Mirena IUD Homepage | Official Website |access-date=19 July 2012 |url-status=live |archive-url=https://web.archive.org/web/20120731015857/http://www.mirena-us.com/ |archive-date=31 July 2012 }}, Bayer Pharmaceuticals. The cylinder of the device is coated with a membrane that regulates the release of the drug.{{cite journal | vauthors = Luukkainen T | title = Levonorgestrel-releasing intrauterine device | journal = Annals of the New York Academy of Sciences | volume = 626 | issue = 1 | pages = 43–49 | year = 1991 | pmid = 1905510 | doi = 10.1111/j.1749-6632.1991.tb37898.x | s2cid = 39610456 | bibcode = 1991NYASA.626...43L }} Bayer markets Skyla as Jaydess in the United Kingdom.{{cite web|last1=Bayer Group|title=What is Jaydess?|url=http://www.jaydess.co.uk/en/healthcare-professionals/what-is-jaydess/|website=Jaydess|publisher=Bayer PLC|access-date=16 November 2016|archive-url=https://web.archive.org/web/20161117144655/http://www.jaydess.co.uk/en/healthcare-professionals/what-is-jaydess/|archive-date=17 November 2016}} Jaydess releases six micrograms per day and lasts for three years.{{Cite journal | vauthors = Römer T, Bühling KJ | doi = 10.1007/s10304-012-0532-4 | title = Intrauterine hormonelle Kontrazeption | journal = Gynäkologische Endokrinologie | volume = 11 | issue = 3 | pages = 188–196 | year = 2013 | s2cid = 20088018 }} In comparison, oral contraceptives can contain 150 micrograms of levonorgestrel.{{cite book| vauthors = Dean G, Schwarz EB |year=2011|chapter=Intrauterine contraceptives (IUCs)| veditors = Hatcher RA, Trussell J, Nelson AL, Cates Jr W, Kowal D, Policar MS |title=Contraceptive technology|edition=20th revised|location=New York|publisher=Ardent Media|isbn=978-1-59708-004-0|issn=0091-9721|oclc=781956734|pages=147–191}} p.150:{{blockquote|Mechanism of action
Although the precise mechanism of action is not known, currently available IUCs work primarily by preventing sperm from fertilizing ova.²⁶ IUCs are not abortifacients: they do not interrupt an implanted pregnancy.²⁷ Pregnancy is prevented by a combination of the "foreign body effect" of the plastic or metal frame and the specific action of the medication (copper or levonorgestrel) that is released. Exposure to a foreign body causes a sterile inflammatory reaction in the intrauterine environment that is toxic to sperm and ova and impairs implantation.^28,29 The production of cytotoxic peptides and activation of enzymes lead to inhibition of sperm motility, reduced sperm capacite journal and survival, and increased phagocytosis of sperm.^30,31… The progestin in the LNg IUC enhances the contraceptive action of the device by thickening cervical mucus, suppressing the endometrium, and impairing sperm function. In addition, ovulation is often impaired as a result of systemic absorption of levonorgestrel.²³
p. 162:
Table 7-1. Myths and misconceptions about IUCs
Myth: IUCs are abortifacients. Fact: IUCs prevent fertilization and are true contraceptives.}} The hormonal IUD releases the levonorgestrel directly into the uterus, as such its effects are mostly paracrine rather than systemic. Most of the drug stays inside the uterus, and only a small amount is absorbed into the rest of the body.

File:Mirena in optimal place - schematic.png of a Mirena.]]

File:Mirena in optimal place - ultrasound.jpg showing a Mirena in optimal place in the uterus, as viewed from angle shown in schematic depiction.]]

File:Mirena intrauterine device insertion.jpg

File:Removal of IUD with progestogen.gif

The hormonal IUD is inserted in a similar procedure to the nonhormonal copper IUD, and can only be inserted by a qualified medical practitioner. Before insertion, a pelvic exam is performed to examine the shape and position of the uterus. A current STI at the time of insertion can increase the risk of pelvic infection.{{cite journal | vauthors = Mohllajee AP, Curtis KM, Peterson HB | title = Does insertion and use of an intrauterine device increase the risk of pelvic inflammatory disease among women with sexually transmitted infection? A systematic review | journal = Contraception | volume = 73 | issue = 2 | pages = 145–153 | date = February 2006 | pmid = 16413845 | doi = 10.1016/j.contraception.2005.08.007 | url = https://zenodo.org/record/1258853 | access-date = 6 February 2020 | url-status = live | archive-url = https://web.archive.org/web/20200206031628/https://zenodo.org/record/1258853 | archive-date = 6 February 2020 }} However, routine screening for gonorrhea and chlamydia prior to insertion is not recommended.{{cite journal | vauthors = Curtis KM, Tepper NK, Jatlaoui TC, Berry-Bibee E, Horton LG, Zapata LB, Simmons KB, Pagano HP, Jamieson DJ, Whiteman MK | title = U.S. Medical Eligibility Criteria for Contraceptive Use, 2016 | journal = MMWR. Recommendations and Reports | volume = 65 | issue = 3 | pages = 1–103 | date = July 2016 | pmid = 27467196 | doi = 10.15585/mmwr.rr6503a1 | doi-access = free }} If a person needs screening and there is no evidence of infection on examination or has been previously screened, insertion of the IUD does not need to be delayed.{{cite web|title=CDC - Summary - US SPR - Reproductive Health|url=https://www.cdc.gov/reproductivehealth/contraception/mmwr/spr/summary.html|website=www.cdc.gov|access-date=13 September 2017|language=en-us|date=21 June 2017|url-status=live|archive-url=https://web.archive.org/web/20170913183850/https://www.cdc.gov/reproductivehealth/contraception/mmwr/spr/summary.html|archive-date=13 September 2017}}

During the insertion, the vagina is held open with a speculum, the same device used during a pap smear. A grasping instrument is used to steady the cervix, the length of the uterus is measured for proper insertion with a uterine sound for decreasing chance of uterine perforation with the IUD, and the IUD is placed using a narrow tube through the opening of the cervix into the uterus. A short length of monofilament plastic/nylon string hangs down from the cervix into the vagina. The string allows physicians and patients to check to ensure the IUD is still in place and enables easy removal of the device. Moderate to severe cramping can occur during the procedure, which generally takes five minutes or less. Insertion can be performed immediately postpartum and post-abortion if no infection has occurred.{{cite journal | vauthors = Curtis KM, Tepper NK, Jatlaoui TC, Berry-Bibee E, Horton LG, Zapata LB, Simmons KB, Pagano HP, Jamieson DJ, Whiteman MK | title = U.S. Medical Eligibility Criteria for Contraceptive Use, 2016 | journal = MMWR. Recommendations and Reports | volume = 65 | issue = 3 | pages = 1–103 | date = July 2016 | pmid = 27467196 | doi = 10.15585/mmwr.rr6503a1 | url = https://www.cdc.gov/mmwr/volumes/65/rr/pdfs/rr6503.pdf | access-date = 3 February 2020 | url-status = live | doi-access = free | archive-url = https://web.archive.org/web/20201016231003/https://www.cdc.gov/mmwr/volumes/65/rr/pdfs/rr6503.pdf | archive-date = 16 October 2020 }}

Misoprostol is not effective in reducing pain in IUD insertion.{{cite journal | vauthors = Lopez LM, Bernholc A, Zeng Y, Allen RH, Bartz D, O'Brien PA, Hubacher D | title = Interventions for pain with intrauterine device insertion | journal = The Cochrane Database of Systematic Reviews | volume = 2015 | issue = 7 | pages = CD007373 | date = July 2015 | pmid = 26222246 | pmc = 9580985 | doi = 10.1002/14651858.CD007373.pub3 }}

Removal of the device should also be performed by a qualified medical practitioner. After removal, fertility will return to previous levels relatively quickly.{{cite journal | vauthors = Mansour D, Gemzell-Danielsson K, Inki P, Jensen JT | title = Fertility after discontinuation of contraception: a comprehensive review of the literature | journal = Contraception | volume = 84 | issue = 5 | pages = 465–477 | date = November 2011 | pmid = 22018120 | doi = 10.1016/j.contraception.2011.04.002 }} One study found that the majority of participants returned to fertility within three months.{{cite journal | vauthors = Randic L, Vlasic S, Matrljan I, Waszak CS | title = Return to fertility after IUD removal for planned pregnancy | journal = Contraception | volume = 32 | issue = 3 | pages = 253–259 | date = September 1985 | pmid = 4085244 | doi = 10.1016/0010-7824(85)90048-4 }}

Levonorgestrel is a progestogen, i.e. a progesterone receptor agonist. The hormonal IUD's primary mechanism of action is to prevent fertilization.{{cite journal | vauthors = Ortiz ME, Croxatto HB | title = Copper-T intrauterine device and levonorgestrel intrauterine system: biological bases of their mechanism of action | journal = Contraception | volume = 75 | issue = 6 Suppl | pages = S16–S30 | date = June 2007 | pmid = 17531610 | doi = 10.1016/j.contraception.2007.01.020 }} p. S28:{{blockquote|Conclusions
Active substances released from the IUD or IUS, together with products derived from the inflammatory reaction present in the luminal fluids of the genital tract, are toxic for spermatozoa and oocytes, preventing the encounter of healthy gametes and the formation of viable embryos. The current data do not indicate that embryos are formed in IUD users at a rate comparable to that of nonusers. The common belief that the usual mechanism of action of IUDs in women is destruction of embryos in the uterus is not supported by empirical evidence. The bulk of the data indicate that interference with the reproductive process after fertilization has taken place is exceptional in the presence of a T-Cu or LNG-IUD and that the usual mechanism by which they prevent pregnancy in women is by preventing fertilization.}}{{cite journal | vauthors = ((ESHRE Capri Workshop Group)) | title = Intrauterine devices and intrauterine systems | journal = Human Reproduction Update | volume = 14 | issue = 3 | pages = 197–208 | date = May–June 2008 | pmid = 18400840 | doi = 10.1093/humupd/dmn003 | doi-access = free }} p. 199:{{blockquote|Mechanisms of action
Thus, both clinical and experimental evidence suggests that IUDs can prevent and disrupt implantation. It is unlikely, however, that this is the main IUD mode of action, … The best evidence indicates that in IUD users it is unusual for embryos to reach the uterus.
In conclusion, IUDs may exert their contraceptive action at different levels. Potentially, they interfere with sperm function and transport within the uterus and tubes. It is difficult to determine whether fertilization of the oocyte is impaired by these compromised sperm. There is sufficient evidence to suggest that IUDs can prevent and disrupt implantation. The extent to which this interference contributes to its contraceptive action is unknown. The data are scanty and the political consequences of resolving this issue interfere with comprehensive research.
p. 205:
Summary
IUDs that release copper or levonorgestrel are extremely effective contraceptives... Both copper IUDs and levonorgestrel releasing IUSs may interfere with implantation, although this may not be the primary mechanism of action. The devices also create barriers to sperm transport and fertilization, and sensitive assays detect hCG in less than 1% of cycles, indicating that significant prevention must occur before the stage of implantation.}}{{cite book| vauthors = Speroff L, Darney PD |year=2011|chapter=Intrauterine contraception|title=A clinical guide for contraception|edition=5th|location=Philadelphia|publisher=Lippincott Williams & Wilkins|pages=239–280|isbn=978-1-60831-610-6}} pp. 246–247:{{blockquote|Mechanism of action
The contraceptive action of all IUDs is mainly in the intrauterine cavity. Ovulation is not affected, and the IUD is not an abortifacient.^58–60 It is currently believed that the mechanism of action for IUDs is the production of an intrauterine environment that is spermicidal.
Nonmedicated IUDs depend for contraception on the general reaction of the uterus to a foreign body. It is believed that this reaction, a sterile inflammatory response, produces tissue injury of a minor degree but sufficient to be spermicidal. Very few, if any, sperm reach the ovum in the fallopian tube.
The progestin-releasing IUD adds the endometrial action of the progestin to the foreign body reaction. The endometrium becomes decidualized with atrophy of the glands.⁶⁵ The progestin IUD probably has two mechanisms of action: inhibition of implantation and inhibition of sperm capacite journal, penetration, and survival.}}{{cite book| vauthors = Jensen JT, Mishell Jr DR |title=Comprehensive gynecology |publisher=Mosby Elsevier|year=2012|isbn=978-0-323-06986-1| veditors = Lentz GM, Lobo RA, Gershenson DM, Katz VL |location=Philadelphia|pages=215–272|chapter=Family planning: contraception, sterilization, and pregnancy termination.}} p. 259:{{blockquote|Intrauterine devices
Mechanisms of action
The common belief that the usual mechanism of action of IUDs in women is destruction of embryos in the uterus is not supported by empirical evidence... Because concern over mechanism of action represents a barrier to acceptance of this important and highly effective method for some women and some clinicians, it is important to point out that there is no evidence to suggest that the mechanism of action of IUDs is abortifacient.
The LNG-IUS, like the copper device, has a very low ectopic pregnancy rate. Therefore, fertilization does not occur and its main mechanism of action is also preconceptual. Less inflammation occurs within the uterus of LNG-IUS users, but the potent progestin effect thickens cervical mucus to impede sperm penetration and access to the upper genital track. }} The levonorgestrel intrauterine system has several contraceptive effects, although thickening of the cervical mucus appears to be the primary effect.{{cite journal | vauthors = Sivin I, Stern J, Coutinho E, Mattos CE, el Mahgoub S, Diaz S, Pavez M, Alvarez F, Brache V, Thevenin F | title = Prolonged intrauterine contraception: a seven-year randomized study of the levonorgestrel 20 mcg/day (LNg 20) and the Copper T380 Ag IUDS | journal = Contraception | volume = 44 | issue = 5 | pages = 473–480 | date = November 1991 | pmid = 1797462 | doi = 10.1016/0010-7824(91)90149-a | url = https://repositorio.ufba.br/bitstream/ri/7413/1/vvvvvvvvvvssss.pdf | access-date = 28 December 2023 | url-status = live | archive-url = https://web.archive.org/web/20231122015707/https://repositorio.ufba.br/bitstream/ri/7413/1/vvvvvvvvvvssss.pdf | archive-date = 22 November 2023 }} Other effects include making the inside of the uterus become fatal to sperm{{cite journal | vauthors = Guttinger A, Critchley HO | title = Endometrial effects of intrauterine levonorgestrel | journal = Contraception | volume = 75 | issue = 6 Suppl | pages = S93–S98 | date = June 2007 | pmid = 17531624 | doi = 10.1016/j.contraception.2007.01.015 }} and thinning of the endometrial lining, but this is not the usual function.{{cite journal | title = Intrauterine devices and intrauterine systems | journal = Human Reproduction Update | volume = 14 | issue = 3 | pages = 197–208 | date = 2008 | pmid = 18400840 | doi = 10.1093/humupd/dmn003 | quote = Both copper IUDs and levonorgestrel releasing IUSs may interfere with implantation | doi-access = free | author1 = ESHRE Capri Workshop Group }}{{cite book| vauthors = Hatcher RA |title=Contraceptive technology|date=2011|publisher=Ardent Media|location=[New York, N.Y.]|isbn=978-1-59708-004-0|page=162|edition=20th rev.|quote=Although the precise mechanism of action is not known, currently available IUCs work primarily by preventing sperm from fertilizing ova.26 IUCs are not abortifacients: they do not interrupt an implanted pregnancy.27 Pregnancy is prevented by a combination of the "foreign body effect" of the plastic or metal frame and the specific action of the medication (copper or levonorgestrel) that is released. Exposure to a foreign body causes a sterile inflammatory reaction in the intrauterine environment that is toxic to sperm and ova and impairs implantation.28,29 The production of cytotoxic peptides and activation of enzymes lead to inhibition of sperm motility, reduced sperm capacite journal and survival, and increased phagocytosis of sperm.30,31… The progestin in the LNg IUC enhances the contraceptive action of the device by thickening cervical mucus, suppressing the endometrium, and impairing sperm function. In addition, ovulation is often impaired as a result of systemic absorption of levonorgestrel}}

Ovulation is not inhibited in all cases.{{cite journal | vauthors = Malik S | title = Levonorgestrel-IUS system and endometrial manipulation | journal = Journal of Mid-Life Health | volume = 4 | issue = 1 | pages = 6–7 | date = January 2013 | pmid = 23833526 | pmc = 3702070 | doi = 10.4103/0976-7800.109625 | doi-access = free }}

Numerous studies have demonstrated that IUDs primarily prevent fertilization, not implantation. In one experiment involving tubal flushing, fertilized eggs were found in half of women not using contraception, but no fertilized eggs were found in women using IUDs.{{cite journal | vauthors = Alvarez F, Brache V, Fernandez E, Guerrero B, Guiloff E, Hess R, Salvatierra AM, Zacharias S | title = New insights on the mode of action of intrauterine contraceptive devices in women | journal = Fertility and Sterility | volume = 49 | issue = 5 | pages = 768–773 | date = May 1988 | pmid = 3360166 | doi = 10.1016/S0015-0282(16)59881-1 }} IUDs also decrease the risk of ectopic pregnancy, which further implies that IUDs prevent fertilization.

file:Mirena IUD with hand.jpg

Hormonal IUDs were developed in the 1970s following the development of the copper IUD in the 1960s and 1970s.{{cite journal | vauthors = Thiery M | title = Pioneers of the intrauterine device | journal = The European Journal of Contraception & Reproductive Health Care | volume = 2 | issue = 1 | pages = 15–23 | date = March 1997 | pmid = 9678105 | doi = 10.1080/13625189709049930 }} Dr. Antonio Scommenga, working at the Michael Reese Hospital in Chicago, discovered that administering progesterone inside the uterus could have contraceptive benefits. With knowledge of Scommegna's work, a Finnish doctor, Jouni Valter Tapani Luukkainen, created the T-shaped IUD that released progesterone, marketed as the Progestasert System in 1976. This IUD had a short, 1-year lifespan and never achieved widespread popularity. Following this relative lack of success, Dr. Luukkainen replaced the progesterone with the hormone levonorgestrel to be released over a five-year period, creating what is now Mirena.{{cite journal | vauthors = Thiery M | title = Intrauterine contraception: from silver ring to intrauterine contraceptive implant | journal = European Journal of Obstetrics, Gynecology, and Reproductive Biology | volume = 90 | issue = 2 | pages = 145–152 | date = June 2000 | pmid = 10825633 | doi = 10.1016/s0301-2115(00)00262-1 }}

The Mirena IUD was studied for safety and efficacy in two clinical trials in Finland and Sweden involving 1,169 women who were all between 18 and 35 years of age at the beginning of the trials. The trials included predominantly Caucasian women who had been previously pregnant with no history of ectopic pregnancy or pelvic inflammatory disease within the previous year. Over 70% of the participants had previously used IUDs.{{cite web|title=Mirena - levonorgestrel intrauterine device |url=https://dailymed.nlm.nih.gov/dailymed/archives/fdaDrugInfo.cfm?archiveid=12313|publisher=Bayer Health Pharmaceuticals|access-date=18 June 2015 |archive-url=https://web.archive.org/web/20150618101430/https://dailymed.nlm.nih.gov/dailymed/archives/fdaDrugInfo.cfm?archiveid=12313 |archive-date=18 June 2015 |date=May 2009}}

In 2013 Skyla, a lower dose levonorgestrel IUD effective for up to three years, was approved by the FDA.{{cite web | url = https://www.accessdata.fda.gov/scripts/cder/daf/ | title = FDA drug approval for Skyla | url-status = dead | archive-url = https://web.archive.org/web/20140813131107/http://www.accessdata.fda.gov/scripts/cder/drugsatfda/index.cfm?fuseaction=Search.DrugDetails | archive-date = 13 August 2014 }} Skyla has a different bleeding pattern than Mirena, with only 6% of women in clinical trials becoming amenorrheic (compared to approximately 20% with Mirena).

The city of Turku, Finland, is currently the only production site for the Mirena contraceptive family.{{Cite web| vauthors = Laitinen K |title=Bayer|url=https://businessfinland.fi/en/whats-new/cases/2017/bayer|access-date=21 September 2021|website=businessfinland.fi|language=en-US|archive-date=21 September 2021|archive-url=https://web.archive.org/web/20210921102847/https://www.businessfinland.fi/en/whats-new/cases/2017/bayer}}

In 2009, Bayer, the maker of Mirena, was issued an FDA Warning Letter by the United States Food and Drug Administration for overstating the efficacy, minimizing the risks of use, and making "false or misleading presentations" about the device.{{cite web|title=2009 Warning Letters and Untitled Letters to Pharmaceutical Companies|url=https://www.fda.gov/Drugs/GuidanceComplianceRegulatoryInformation/EnforcementActivitiesbyFDA/WarningLettersandNoticeofViolationLetterstoPharmaceuticalCompanies/ucm055773.htm|publisher=U.S. Food and Drug Administration|access-date=18 June 2015|url-status=dead|archive-url=https://web.archive.org/web/20150618092226/https://www.fda.gov/Drugs/GuidanceComplianceRegulatoryInformation/EnforcementActivitiesbyFDA/WarningLettersandNoticeofViolationLetterstoPharmaceuticalCompanies/ucm055773.htm|archive-date=18 June 2015}}{{cite magazine| vauthors = Bekiempis V |title=The Courtroom Controversy Behind Popular Contraceptive Mirena|url=http://www.newsweek.com/2014/05/02/courtroom-controversy-behind-popular-contraceptive-mirena-248443.html|magazine=Newsweek|access-date=18 June 2015|date=24 April 2014|url-status=live|archive-url=https://web.archive.org/web/20150618101048/http://www.newsweek.com/2014/05/02/courtroom-controversy-behind-popular-contraceptive-mirena-248443.html|archive-date=18 June 2015}} From 2000 to 2013, the federal agency received over 70,072 complaints about the device and related adverse effects.{{cite web| vauthors = Budusun S |title=Thousands of women complain about dangerous complications from Mirena IUD birth control|work=newsnet5 |date=18 June 2013 |url=http://www.newsnet5.com/news/local-news/investigations/thousands-of-women-complain-about-dangerous-complications-from-mirena-iud-birth-control|publisher=ABC Cleveland|access-date=18 June 2015|archive-url=https://web.archive.org/web/20150618101120/http://www.newsnet5.com/news/local-news/investigations/thousands-of-women-complain-about-dangerous-complications-from-mirena-iud-birth-control|archive-date=18 June 2015}}{{cite web| vauthors = Colla C |title=Mirena birth control may be causing complications in women|work=KNXV |url=http://www.abc15.com/news/national/mirena-birth-control-may-be-causing-complications-in-women|publisher=ABC 15 Arizona|access-date=18 June 2015|date=21 May 2013|archive-url=https://web.archive.org/web/20150618063056/http://www.abc15.com/news/national/mirena-birth-control-may-be-causing-complications-in-women|archive-date=18 June 2015}} As of April 2014, over 1,200 lawsuits have been filed in the United States.{{cite magazine| vauthors = Bekiempis V |title=The Courtroom Controversy Behind Popular Contraceptive Mirena|url=http://www.newsweek.com/2014/05/02/courtroom-controversy-behind-popular-contraceptive-mirena-248443.html|magazine=Newsweek|access-date=16 November 2016|date=24 April 2014|url-status=live|archive-url=https://web.archive.org/web/20161115213808/http://www.newsweek.com/2014/05/02/courtroom-controversy-behind-popular-contraceptive-mirena-248443.html|archive-date=15 November 2016}}{{cite web|title=Popular contraceptive device Mirena target of lawsuits in Canada, U.S|url=http://www.ctvnews.ca/health/health-headlines/popular-contraceptive-device-mirena-target-of-lawsuits-in-canada-u-s-1.1832588|publisher=CTV|access-date=16 November 2016|date=21 May 2014|url-status=live|archive-url=https://web.archive.org/web/20161026180840/http://www.ctvnews.ca/health/health-headlines/popular-contraceptive-device-mirena-target-of-lawsuits-in-canada-u-s-1.1832588|archive-date=26 October 2016}}{{cite magazine| vauthors = Blackstone H |title=When IUDs Go Terribly Wrong|url=https://www.vice.com/en/article/when-iuds-go-terribly-wrong-mirena/|magazine=Vice|access-date=16 November 2016|date=31 May 2016|url-status=live|archive-url=https://web.archive.org/web/20161117072244/https://broadly.vice.com/en_us/article/when-iuds-go-terribly-wrong-mirena|archive-date=17 November 2016}}

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