Just wanted to add my twopence-worth. I had a Mirena fitted to combat severe endometriosis....the pain stopped completely (great) as did my periods (also great), BUT the weight piled on. I've gone from a size 10/12 to a size 14 and am absolutely dreading creeping up to a 16, purely because it makes me so miserable and depressed (I'm tall so can cover it up a bit, I suppose, but I just don't feel like 'me' any more).
But I have to say, only by dint of eating rigidly controlled, very low-calorie meals can I even maintain my weight, let alone lose any. Having kept my weight stable by eating 'normally' for over 20 years (and losing a bit whenever I felt like it, just by cutting down in a fairly minor way), it's dismaying to say the least. And I actually prefer salads and healthy food, never eat puddings, take regular exercise, etc, etc.
At least my specialist didn't laugh at me, which has been the fate of so many other women, but he did say I might have put on the weight because I'm not in pain, am happier, and am therefore eating more. I honestly don't think so. I do think it's the Mirena.