Hi - I have just stumbled across this website. I was diagnosed a couple of years ago with an under-active thyroid (not sure of the levels) and I am taking 100mg of levothyroxine. Due to a chance encounter the other day, I have realised that my gradual weight gain over the last few years could be down to this medication. I don't really think I over-eat, but have gone from a UK size 10 up to a 16/18 and have given up trying to cut down on food as it seems to make no difference. Could someone please explain what Thyroid S is and if you can get it without going to the doctor and also NDT and what is T3? I am seriously thinking of stopping the levo (after reading comments) and trying something else?