I've got to say that Mirena makes my hair very thick, and I have lost weight, not gained it...and I LOVE not having periods.
I have had mood swings, irritability, and stomach issues since having it installed in July'07 but no other problems what so ever, until a few months ago...ever since May'09 I have had nausea, extreme loss of appetite, and breakouts(very out of character for me). My husband had a vasectomy in May, and I plan on getting the Mirena removed next month. The ongoing irritability is definitely the biggest problem for me...it makes me very short tempered with my children.
I don't know why the new symptoms started a few months ago...maybe some kind of hormonal buildup...I am very sensitive to birth control usually, and Mirena has served its purpose well, but now I am ready to move on.
I think Mirena is like any birth control, it works well for some people and not at all well for others. I do not think it is awful, or terrible or anything like that...it just has to be the right fit, and all drugs have side effects. Good luck ladies!!