A.C.
The Mirena is a smooth plastic t shaped IUD. It works by thinking the lining to your uterus and releasing small amounts of hormones to prevent inplantation. I have had it in for over a year now the first 6 months my uterus fluttered and i had no periods , but after my body was use to it i have a few days of spotting when i'm suppose to have my period and no problems... but remember every persons body is different I know of one lady who had to take hers out because her body rejected the foreign object..
And I've only heard a few thing with the paragard. but because it is copper it can react with your body chemistry and make your periods heavy or cramping worse.