Hi, Levothyroxine is a medicine that is used in the treatment of underactive thyroid or hypothyroidism. Levothyroxine may cause extreme fatigue and tiredness as less side effects of this medication. Despite having side effects you shouldn t stop it without consulting your doctor. If side effects persist, inform your prescribing doctor. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician