From the Guidelines
The Mirena IUD does contain hormones, specifically levonorgestrel, a type of progestin, which is released directly into the uterus. The Mirena contains 52 mg of levonorgestrel and releases approximately 20 micrograms per day initially, gradually decreasing to 10 micrograms per day after 5 years 1. This localized hormone release works by thickening cervical mucus to prevent sperm from reaching the egg, thinning the uterine lining, and sometimes preventing ovulation. Unlike combined hormonal contraceptives, Mirena doesn't contain estrogen, which means it may cause fewer systemic hormonal side effects.
Key Points
- The hormonal component makes Mirena highly effective at preventing pregnancy (over 99% effective) and also helps reduce menstrual bleeding, with many users experiencing lighter periods or no periods at all 1.
- Mirena is approved for use for up to 7 years for contraception and 5 years for treating heavy menstrual bleeding 1.
- The use of Mirena in adolescents is considered safe and effective, with a low risk of complications, including pelvic inflammatory disease 1.
Benefits and Risks
- The benefits of using Mirena include its high effectiveness in preventing pregnancy, reducing menstrual bleeding, and improving symptoms of painful menses 1.
- The risks associated with Mirena are generally low, but may include pelvic pain, expulsion of the device, and changes in menstrual bleeding patterns 1.
From the Research
Mirena IUD and Hormones
- The Mirena IUD releases a small daily dose of a progestin, levonorgestrel, into the uterine cavity 2.
- The local delivery of levonorgestrel maintains the endometrium in a nonproliferative state and reduces the number of bleeding days 3.
- The circulating levels of levonorgestrel are very low, but minor side effects related to the androgenic properties of levonorgestrel have been reported 3.
- The Mirena IUD has been advocated as a means of delivering progestogen to the endometrium as part of combined hormone replacement therapy 4.
Effects of Mirena IUD on Hormone-Related Conditions
- The Mirena IUD may have a role in the treatment of other benign gynecological disorders, such as adenomyosis or endometriosis 4.
- The use of the Mirena IUD is associated with a decreased risk of endometrial cancer, ovarian cancer, and cervical cancer 5.
- However, the use of the Mirena IUD is also associated with a slightly increased risk of breast cancer, particularly among women with a family history of breast cancer 5.
Mechanism of Action
- The precise mechanism of breakthrough bleeding during the first months of Mirena IUD use is unclear, but it may be related to a direct effect of levonorgestrel on endometrial vascular development 4.
- The Mirena IUD provides an effective contraception by maintaining the endometrium in a nonproliferative state and preventing ovulation 3, 6.