The levonorgestrel-releasing IUD is a T-shaped polyethylene device. The frame is 32 millimeter in both the horizontal and the vertical directions. The cylindrical reservoir around the vertical stem contains a mixture of silicone and 52 mg of levonorgestrel, a progestin widely used in implants, oral contraceptives, and vaginal rings.

25 microgram of levonorgestrel is released every day. A monofilament removal thread is attached to a loop at the end of the vertical stem. Mirena is packaged within a newly designed inserter, which is discarded after use. Mirena has an effective life of 5 years. Like other copper bearing IUDs, Mirena can be inserted within the first seven days of onset of menstruation.

There are at least three levonorgestrel-releasing IUD principles: causing thick cervical mucus which inhibits the passage of sperm through the cervical canal; causing anovulation in about 25 per cent women; and causing high levonorgestrel levels in the uterine cavity, which suppress estradiol receptors and produce an atrophic endometrium, and inhibit passage of sperm through the uterine cavity.

The levonorgestrel-releasing IUD use has many advantages over the copper IUDs. It is highly effective with the first year failure rate of 0.1 per cent and five year cumulative failure rate of 0.7 per cent. There is a marked reduction in menstrual blood loss and the systemic level of hormone is very low as compared to the other progesterone only methods. Mirena provides dramatic relief in dysmenorrhea. Once inserted it is effective for 5 years and fertility returns rapidly on discontinuation.

Eighty per cent of the women intending to get pregnant will become pregnant within 12 months of discontinuing the levonorgestrel-releasing IUD. This is comparable with pregnancy rates following discontinuation of other barrier contraceptive methods. Mirena has many noncontraceptive benefits. It has beneficial effect on menorrhagia, dysmenorrhea and reduces the risk of pelvic inflammatory disease. It also reduces the risk of endometrial cancer by 50%.

Though the fact that the levonorgestrel-releasing IUD contains levonorgestrel the women having active liver disease, liver tumor, known or suspected carcinoma of the breast or genital actinomycosis should not use Mirena. Women with diabetes and using the levonorgestrel-releasing IUD should monitor their blood glucose level more regularly.

Expulsion rates for the levonorgestrel-releasing IUD are little higher than copper IUDs. The ovarian cysts are three times more common in Mirena users: 1.2 percent of the levonorgestrel-releasing IUD users develop ovarian cysts as compared to 0.4 percent of non users. Particularly during the first three months could be disturbing to many women and up to 20 per cent of women develop amenorrhea by the end of the first year of use and may not be acceptable to many women.

The levonorgestrel-releasing IUD should be removed if a woman develops migraine or focal neurological conditions, severe headaches, jaundice, increased blood pressure, stroke or myocardial infarction. Or if repeating the words five times really fast gives you a headache.