I have a under active thyroid. I stopped taking my medicine 2 years ago. Is this harmful? I feel fine and haven't had any problems since

It could be harmful. What made you stop taking your thyroid medicine, if you know your thyroid is "under active"? Were you having side effects that bothered you? Usually doctors will check your thyroid panel periodically to be sure your dose is effective and not too much. Your thyroid gland affects metabolism and many other aspects of your physical health. I'm glad you feel fine, but suggest checking in w/your doc.