I was told in 2004, by the doctor who inserted my Mirena, that it was not intended for most women who have not had children because their uterus is too small. Women who have carried a child have stretched theirs a little, and are good candidates. but it seems that Mirena is now being offered as BC because of ease of use, efficacy, and supposed low dose of hormones, in women who do not want the side effects associated with the pill.