I lost 40 pounds on Mirena. I looked gaunt and sick. It didn't matter what I ate-sometimes I was ravenous, sometimes I had no appetite at all-I continuously lost a pound every week and a half. NEVER gained.
I think for the most part it was that I wasn't absorbing anything I ate, but it was also that I had polyuria. I could not hold water in my body. I had to pee constantly.