Just thought I'd post with my input. I was diagnosed with mild hypothyroidism a year BEFORE having Mirena put in. I've been on a consistent dose of euthyrox during the whole Mirena debacle.
For me, the Mirena did not effect my thyroid levels as I've seen doctors consistently and my levels held steady. Hopefully a correct diagnosis will help some of you, but I do want to caution you that, for me, none of my Mirena symptoms were stopped or lessened because of it. However, who knows, things might have been worse if I wasn't already on medicine. Thyroid problems are so difficult to get diagnosed because symptoms and levels can vary so widely. So many people on this forum have mentioned thyroid symptoms, I really am wondering if we've started to find the answer as to why we have such problems with Mirena when other women have good experiences.