As someone who takes thyroid hormone supplement (Synthroid) because of an underactive thyroid, I can tell you that the hormone supplements are very slow acting. When I had to get my first nuclear medicine thyroid scan, I was already taking Synthroid. I had to go off it and stay off it for four weeks before I could get the scan, to avoid results that might be affected by the Synthroid. So if you start taking it, wait a few weeks to see how you respond to it, and then let your doctor know. It could be that the dose needs to be adjusted.