I just started taking levothyroxine (generic synthroid) last November. By the time they put me on it I was having severe bhypothyroid symptoms, as they had not tested me in a year (although I thought they had tested me over the summer). I was constantly exhausted, could not get warm, etc. In the two months since then I have gotten most of my energy back and don't get chilled so easily.

My understanding is that synthroid, in the correct dose, has very few side effects you need to watch out for. The trick to keeping your thyroid stable with it is you have to always take it on a completely empty stomach and not have anything in your stomach for an hour after taking it--even having a morning cup of coffee after taking it can disrupt it's effectiveness!

You are definitely not alone, though. My understanding is this is a pretty common after-effect of radiation to the neck.

Nelie