Originally Posted by mrsD

The best way to know for sure is to stop the iodine for 2 or so weeks. Stop all the supplements too during that time.

If you slip back again, then start only with the 300mcg of iodine.
If you respond well then that is your answer.

Iodine is used to make thyroid hormone.

Here is a good monograph of what Iodine does, and how much you can take safely. 300mcg is well below the recommended upper limit of 1,100mcg.