 [ Symptoms ] is it possible for a therapeutic overdose of synthroid to cause weightloss  i have been on synthroidlevothyroxine for years over the past year i lost on purpose 45 pounds now i cannot maintain my weight i have increased my calories by half and still am losing weight could this be because my synthroid dose is no longer appropriate for my weight [ Disease ] hi if you see your doctor and work with him you could be on the wrong hormone so it would mean coming off what your on give it a few days and get a blood test from this they should be able to tell which your low on and re start from there and see how you go then do hope this helps good luck