Check with your doctor immediately if any of the following side effects occur while taking levothyroxine:
Less common
  • Chest pain or discomfort
  • decreased urine output
  • difficult or labored breathing
  • difficulty with swallowing
  • dilated neck veins
  • extreme fatigue
  • fainting
  • fast, slow, irregular, pounding, or racing heartbeat or pulse
  • fever
  • heat intolerance
  • hives or welts