As one who has been HypoT for over 25 years, and w/Hashi's for the last 8, I can assure you that I've been on the synthroid all that time successfully.
The Hashi's issue is an auto-immune one that followed two other AI issues, so no connection to the synthroid-dose just changed. Get tested for Free T3&T4 every 6 months and adjusted accordingly.
An interesting site to learn about the THYROID and other glands is the following: http://www.endocrineweb.com/endocrin...docrine-system
I find it fascinating that other glands at times pick up the slack of thyroid and other gland malfunctions. These teeny glands can make our life happy or totally miserable depending on how well they work and work together.
Good luck and keep us up to date please! - j