 [ 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 ] also if you are losing too much weight some loss will happen then your doctor needs to change your dosage or try a new medicine for you