I have been on Thyroxine for years but want to try Nature Throid, as I think it might be better for me, as it contains calcitonin. However, I have noticed that lots of people here suggest getting Ferritin levels at least 70 before starting. I have low Ferritin, and just below mid B12. If I'm already taking Thyroxine on these levels, and surviving, what's the difference between taking Thyroxine and NDT when thinking about Ferritin levels? what difference will it make? Will there be a different reaction, and why?