Mirena is an intrauterine device system IUD or IUS which release a progesterone called levonorgestrel into the uterus and prevents pregnancy

The Mirena intrauterine device or IUD contains levonorgestrel which is a progestogen used in a variety of contraceptive products. After the Mirena IUD has been inserted, low doses of levonorgestrel can be administered into the uterine cavity with the MIRENA intrauterine delivery system.

MIRENA has mainly local progestogenic effects in the uterine cavity and studies of MIRENA prototypes have suggested several mechanisms that prevent pregnancy:

• thickening of cervical mucus preventing passage of sperm into the uterus,
• inhibition of sperm capacitation or survival, and
• alteration of the endometrium.

Ovulation is inhibited in some women using MIRENA. In a 1-year study approximately 45% of menstrual cycles were ovulatory and in another study after 4 years 75% of cycles were ovulatory.