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 women with 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. 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. Breastfeeding
Progestogen-only contraceptives such as an IUD are not believed to affect milk supply or infant growth. 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%).When using Mirena, about 0.1% of the maternal dose of levonorgestrel can be transferred via milk to the
nursed infant. 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.
In addition to birth control, the hormonal IUD is used for prevention and treatment of:

Heavy menstrual periods
Endometriosis and chronic pelvic pain
Adenomyosis and dysmenorrhea
Anemia
Endometrial hyperplasia (especially in pre-menopausal women who wish to maintain fertility in the treatment of endometrial hyperplasia)
In some cases, use of a hormonal IUD may prevent a need for a hysterectomy.Advantages:

Considered one of the most effective forms of reversible birth control
Can be used while breastfeeding (see also nursing mothers)
No preparations needed before sex, though routine checking of the device strings by patient and physician is advised to ensure proper placement remains intact
90% of users who wish to become pregnant do so within 24 months of removal. May experience lighter periods (some women stop having periods completely, see also amenorrhea)
Effective for up to three to seven 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

Effectiveness
After insertion, Mirena is effective at preventing pregnancy for up to seven years. Kyleena is approved for five years and Skyla is approved for three years.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%. These rates are comparable to tubal sterilization, but unlike sterilization the effects of the hormonal IUD are reversible.