I have noticed that a few days after I started the Methimazole, I started having what could be heartburn but it was at the base of my neck/throat area (around where my thyroid is). I went back on my Zantac and after a few days it subsided. Now my Meth. dosage has been increased to three times a day and I have noticed that feeling come back/increase. Its odd though. It only happens shortly after I take my Meth. Truthfully it makes me wonder if it is working instantly on the thyroid, since I am only having this feeling in this area. Additional antacids aren't touching it. Has anybody else experienced this? Maybe its just a form of heartburn from the med. Hmm...