Many patients suffering from primary hypothyroidism ask whether taking long-term levothyroxine will have adverse side effects. Well, levothyroxine just replaces the deficiency of thyroid hormone in your body, it does the functions which thyroid hormone would have done in your body if you did not have a thyroid hormone deficiency. So the question of side effects doesn't arise, as its just a replacement of what your body is deficient in. However, a dose of levothyroxine needs to be titrated before maintaining TSH within normal limits. After initiation of thyroxine, TSH is rechecked in 4-6 weeks and dose adjusted. once TSH COMES IN NORMAL RANGE , thereafter it is checked on an annual basis and dose altered if needed. PLEASE DO NOT STOP , INCREASE OR DECREASE LEVOTHYROXIN without asking your doctor.