General Information

Mirena is a hormone-releasing system placed in the uterus to prevent pregnancy for up to five years. Mirena works by delivering a low dose of the progestin levonorgestrel directly to the lining of the uterus. Prevention of pregnancy may be due to subsequent thickening of cervical mucus, which prevents the passage of sperm, inhibition of sperm mobility and inhibition of endometrial growth.

Mirena has been available for ten years in Europe and has been used by approximately two million women worldwide. Berlex Laboratories will market Mirena under a license from The Population Council, which initially developed the contraceptive.

Clinical Results

Two large trials of Mirena conducted in Finland and Sweden consisted of a predominately Caucasian trial population, and over 70% of the participants had previously used IUDs. Results from 1169 women 18 to 35 years of age who used Mirena for up to five years indicated that the drug produced 12-month pregnancy rates less than or equal to 0.2 per 100 women. Additionally, the cumulative 5-year pregnancy rate was approximately 0.7 per 100 women. However, due to limitations of the available data a precise estimate of the pregnancy rate is not possible. (from Mirena Physician Insert)

Side Effects

In clinical trials, side effects of Mirena were most common during the first months after insertion and subsided during prolonged use. Side effects associated with Mirena include (but are not limited to) the following:

Acne

Back pain

Breast tenderness

Headaches

Mood changes

Nausea

Like many contraceptives, Mirena does not protect against HIV infection (AIDS) and other sexually transmitted diseases.

In addition to preventing pregnancy, Mirena use may result in a change in bleeding patterns. There may be an increase in intermenstrual bleeding in the first three to six months following insertion. After this, a woman's period may become shorter and lighter. Some women experience an absence of menstrual bleeding after one year.

Use of IUDs has been associated with an increased risk of pelvic inflammatory disease (PID). The highest risk of PID occurs shortly after insertion (usually within the first 20 days). Please contact a health care provider for a complete list of possible Mirena side effects or for more information.

Mechanism of Action

The local mechanism by which continuously released levonorgestrel enhances contraceptive effectiveness of the IUD has not been determined. Studies suggest several mechanisms that prevent pregnancy: thickening of cervical mucus, inhibition of sperm mobility and inhibition of endometrial growth. (from Mirena Physician Insert)