How Your Mirena IUD Works: For Contraception, For Lightening Period Bleeding, and For Endometriosis

Women are protected against pregnancy the day of insertion of their Mirena IUD. Many who use the IUD want to know just exactly how the Mirena IUD works to be a contraceptive. Failure rares are extraordinarily low with a pregnancy rate of about 0/2% in Mirena users!  Immediately the IUD, which has a progesterone called levonorgesterel (or nick named the LNG-IUS) begins immediately to release the hormone at a rate of about 20 mcg/day. For most women the hormone dose is down by about half at the end of the five years. And the blood level of the hormone itself can range quite a bit between women. There are some women who have much higher blood levels, for instance endometriosis is a condition that leads to higher levels, which may in fact be why women with endometriosis do get some relief from this Mirena device. The hormone release changes the cervical mucus and the cervix itself rapidly becomes impenetrable by sperm. This amount of progesterone hormone is not enough to affect the levels of estrogen. So it will never decrease estrogen related menstrual cycle symptoms, but it also will allow women to keep enough estrogen production to preserve bone. If you have had a Mirena and you had no abnormal bleeding, but now you have irregular periods it may mean the device has slipped or changed position, it's not so much related to your blood levels of hormones. Actually women who stop getting their periods and women who continue to get their periods have the same hormone blood levels. But it is this very light bleeding, or no bleeding during the menstrual period that produces relief of menstrual cramps and protects women from the pain of endometriosis and the pain of the condition adenomyosis (glands of the lining entrapped within the wall of the uterus). It may even be why some women with pelvic congestion syndrome get relief from the Mirena IUD. The progesterone hormone in the IUD may have an effect on the vaginal health. Some studies report that new users may get more yeast infections, but some studies don't actually document any real change in the type of bacteria or amount of yeast organisms in the vagina after beginning Mirena use. Most women won't get enough hormone to change their blood chemistry or blood fat levels, but actually one study did show a lower cholesterol level in Mirena users. We don't think these changes in blood or vaginal chemistry affects the way it works for contraception. We think that the changes of the lining of the uterus, and the changes in chemicals within the glands of the uterus itself prevents eggs from being fertilized by sperm. The Mirena IUD system is complex, but we have a much better medical understanding on how it works to cure heavy periods, cure menstrual cramps, help relieve the pain of endometriosis, and to effectively prevent pregnancy. It is an excellent choice, therefore, for many women.
Updated information from the Review article on levonorgesterel-releasing IUS for contraception in the March 2012 issue of Contraception.


  1. Thanks for your efforts and information on your site. Do you have any answers as to why Mirena did the opposite for me what it was supposed to do? On Mirena I had for 5 months my period every 2-3 weeks and it lasted 10-12 days. That 5th month I menstruated the entire month. 4 weeks. That's when I had the Mirena removed and underwent endometrial ablation which I just had and have fingers crossed it's the answer. I'm 45, in perimenopause. Had one child at age 41. I struggled in my youth to find the right BCP and finally Yasmin was the perfect one for me. Didn't make me bloated or sluggish, didn't lower libido and made my periods lighter. But I didn't want to go back on it for fear of blood clots. I'd had heavy periods all my life but it was after going off Yasmin at 38 that they really got bad to the point of giving me anemia. I'm just wondering what I should be doing now in terms of hormone replacement or what. I'm thin, not overweight but I do need to eat better and exercise; I'm busy raising a 4 year old and neglect myself. Should I perhaps go back on Yasmin? Thanks for any answers or suggestions you may have.

  2. Women who find that their Mirena IUD is working to control menstrual periods and contraception can still consider taking an oral contraceptive pill for the management of perimenopausal symptoms. Perimenopause is a time of transition and thus evaluation has to occur over time. For our patients at Women's Health Practice, if someone presents with perimenopausal symptoms we offer evaluation and testing to diagnose the cause and nature of the symptoms. Once a diagnosis is reached we can entertain the decision to treat with hormones if it can be done safely. The risk of deep vein clotting or other vascular accidents is affected by many parameters including a genetic predisposition to clots, whether a woman smokes, her level of cardiovascular disease and blood inflammation to name a few. Testing can determine parts of this information ad at Women's Health we offer these evaluations.

  3. I am one of the unfortunate women who got yeast infections. My doctor didn't believe me it was the IUD, but it definitely was. I had the IUD inserted for long periods due to polyps. I had lots of clots during my long period and lots of spotting between periods. I had so many polpys the doctor couldn't remove them all during the polypectomy and D&C. Pathology was normal. I tried the IUD. For the first 6 months, I spotted or bled nearly every day. For the next 6 months, the IUD was fabulous! My clotty periods went away and I had barely any spotting. I only saw bleeding for like 7-8 days a month! I thought it was a miracle! Then, when I'd had it in for about a year, I got my first ever yeast infection. We treated it and I thought that was it. The next month, I got another yeast infection and it continued on like this for the next 6 months. A near constant yeast infection on the days I wasn't bleeding. I finally had my doctor remove the IUD even though she claimed it wasn't causing the yeast infections. After removal, I have not had one yeast infection in the nearly year it has been. My period was manageable for a while, but I'm now back to my clotty periods and spotting all throughout the month. I guess I can either deal with it or proceed to the endometrial ablation. I'm only 36 so that might not be a great option for me.

  4. My daughter, 21 years old, got the Mirana inserted 3 days ago. She is saying that there is white fleshy discharge and is panicked. She will call her doctor tomorrow, but in the meantime, if this is normal I would like to let her know so she doesn't continue to worry.

  5. Generally speaking any one with a vaginal discharge, aside from one they are very sure is a yeast infection, should be examined by a physician. Check with your gynecologist's office for their criteria of emergency. For our patients, we try to see them the same day if they are having acute symptoms, particularly after an IUD insertion.


Post a Comment

Thank you for your comments and questions. This blog is not intended to replace medical care, but is informational only. We hope you will become a follower or visit Womens Health Practice. We offer a variety of unique services including MonaLisa Touch, Coolsculpting, Labiaplasty, and Gynecoloigic Clinical Research Trials. For more information on menopause see

Popular posts from this blog

Passing Your Uterine Lining, Menstrual Period Norms

Mirena IUD and Your Sex Drive

Post-Endometrial Ablation Syndrome