Yes, weight gain with an inability to lose the weight is a side effect of the Mirena, I just found out from my doctor. Usually women are fine the first year but then they start to gain and can\'t take it off. I have gained 15 lbs. even though I exercise 6 days a week and watch what I eat. I have never had a problem with weight gain before. Also, I developed an ovarian cyst that has burst, as well as a lot of acne. I really loved the worry-free sex, but I\'m getting the Mirena taken out in two weeks because there were just too many side effects. Who knows, maybe you\'ll have better luck with it. Good luck!