Max had thyroid issues, think his was overactive as well.
We had to have Vidalta tablets every other day, and regular blood tests to check the Tyroxine levels.
The tablets are tiny, and I used to hide them inside Defurrum treats, as you can break them in half and the tablet used to hide inside the gooey centre, they were a godsend in my house
Post up the blood readings when you get them, but don't worry, thyroid if its in its own is pretty simple to rectify, and the thyroid can also be removed if necessary. Its only trickier to deal with when its combined with kidney issues, which is what we had with Mr Max, and why it was harder to control.
Don't worry