Hypothesis: Pretreatment with mifeprsitone prior to Mirena placement will induce amenorrhea and reduce bleeding irrregularities during the initial months of Mirena use.

The levonorgestrel releasing intrauterine system (IUS), Mirena, represents a highly effective contraceptive method that is cost-effective and requires limited patient effort. Furthermore Mirena offers numerous noncontraceptive benefits and addresses different medical needs for women in reproductive and non reproductive age. Side effects such as menstrual abnormalities are important reasons for early discontinuation of a contraceptive method. Irregular bleeding pattern and spotting represents a well known adverse effect during the first months of use with Mirena and corresponds to the most important factor that negatively influences the acceptability of the IUS. Up to today no standard treatment has been suggested to resolve this issue.

By inducing amenorrhea within a short period of treatment with an anti-progesterone, mifepristone, prior to insertion of Mirena, the bleeding irregularities during the first months of use might be reduced and could therefore represent an important strategy for increasing acceptability of this contraceptive system.

The purpose of the present study is to evaluate the bleeding pattern during the first months of use of Mirena in patients treated with mifepristone compared to placebo in women using Mirena for contraception. The study will also address the effect of mifepristone on endometrial morphology and breast tissue.

Inclusion criteria:

• Pre-menopausal women, >/= 18 years of age.
• Desire of Mirena for contraception
• Good general health (as judged by; general physical examination
• Willing and able to participate after giving informed consent

Exclusion criteria:

• Any hormonal treatment or IUD use within 2 months prior to study start
• History of malignant disorder of the breast
• Any contraindication to mifepristone
• Pregnancy or breast feeding within 2 months prior to study start